Distinctions Between CD8+ and CD4+ T-Cell Regenerative Pathways Result in Prolonged T-Cell Subset Imbalance After Intensive Chemotherapy

In vitro susceptibility of CD4+ and CD8+ T cell subsets to fludarabine

Administration of the adenosine analogue fludarabine (FLU) in vivo induces a profound and prolonged T lymphopenia which mainly affects CD4(+) cells. To better understand the mechanistic basis underlying this preferential depletion, we analyzed the in vitro susceptibility of T cell subsets to FLU-induced apoptosis. Contrasting with observations in vivo, our results showed that treatment of peripheral blood mononuclear cells with FLU induced a higher level of apoptosis in CD8(+) than in CD4(+) T lymphocytes. This increased sensitivity of CD8(+) T cells to FLU was observed in samples from both, healthy donors and B cell chronic lymphocytic leukemia patients, and resulted in higher CD4:CD8 ratios in FLU-treated than in untreated cultures (P<0.01). Expression of factors involved in FLU transport and metabolism was then evaluated by quantitative real time-PCR in normal T cell subsets. It was found that mRNA levels of human equilibrative nucleoside transporter-1 nucleoside transporter were higher whereas deoxycytidine kinase and IMP/GMP selective 5'-nucleotidase mRNA levels were lower in CD4(+) cells. However the dCK/cN-II ratio was 2-fold greater in CD8(+) than in CD4(+) T lymphocytes, which could account for the higher apoptosis levels observed in the CD8(+) subset. These results favor the view that decreased CD4:CD8 ratios in FLU-treated patients should be attributed to differences in cell recovery and/or homing between T cell subsets.

Earlier low-dose TBI or DST overcomes CD8+ T-cell-mediated alloresistance to allogeneic marrow in recipients of anti-CD40L

Treatment with a single injection of anti-CD40L (CD154) monoclonal antibody (mAb) and fully mismatched allogeneic bone marrow transplant (BMT) allows rapid tolerization of CD4+ T cells to the donor. The addition of in vivo CD8 T-cell depletion leads to permanent mixed hematopoietic chimerism and tolerance. We now describe two approaches that obviate the requirement for CD8 T-cell depletion by rapidly tolerizing recipient CD8 T cells in addition to CD4 cells. Administration of donor-specific transfusion (DST) to mice receiving 3 Gy total body irradiation (TBI), BMT and anti-CD40L mAb on day 0 uniformly led to permanent mixed chimerism and tolerance, compared with only 40% of mice receiving similar treatment without DST. In the absence of DST, moving the timing of 3 Gy TBI to day -1 or day -2 instead of day 0 led to rapid (by 2 weeks) induction of CD8+ cell tolerance, and also permitted uniform achievement of permanent mixed chimerism and donor-specific tolerance in recipients of anti-CD40L and BMT on day 0. These nontoxic regimens overcome CD8+ and CD4+ T-cell-mediated alloresistance without requiring host T-cell depletion, permitting the induction of permanent mixed chimerism and tolerance.

Enhanced T-Cell Maturation, Differentiation and Function in HIV-1-Infected Individuals after Growth Hormone and Highly Active Antiretroviral Therapy

Background

Strong virus-specific helper and cytotoxic T-cell responses correlate with non-progression during HIV-1 infection. Administration of antiretroviral therapy (ART) during the chronic phases of HIV-1 infection fails to restore these responses in most patients.

Design and methods

We assessed the changes in immune function of 12 HIV-1-positive individuals treated with ART for over 4 years, who received 4 mg/day of recombinant human growth hormone (rhGH) for 12 weeks and were then randomized into groups receiving either placebo, twice weekly or alternate day dosing of rhGH. Peripheral blood was drawn for phenotypic analysis and functional assays at time points 0, 12 and 24 weeks.

Results

At week 12, we observed significant increases in naive CD4 T cells ( P<0.01) and effector CD8 T cells based on CD45RA and CCR7 expression ( P<0.02). In addition, we observed a rise in HIV-1 antigen-specific CD4 ( P<0.005) and CD8 ( P<0.05) T-cell responses. Twelve weeks post-randomization into placebo, alternate day or twice weekly dosing (24 weeks post-baseline), the phenotype and function of the virus-specific effector CD8 T cells seen at week 12 was maintained in most patients regardless of randomization arm and despite the disappearance of HIV-1-specific CD4 T-cell responses.

Conclusions

Concomitant administration of rhGH at 4 mg/day with highly active ART appears to partially reverse some of the defects exerted on the immune system by HIV-1. This combination may represent a valuable immunotherapeutic intervention aiding in the treatment of chronic HIV-1 infection.

Human cytomegalovirus-specific immunity following haemopoietic stem cell transplantation

The herpesvirus Human Cytomegalovirus (HCMV) is an important opportunistic infection in recipients of allogeneic haemopoietic stem cell transplants, in whom HCMV-specific CD8+ and CD4+ T-cell responses are impaired. The nature of the HCMV-specific T-cell response in healthy virus carriers has been characterised in detail. High frequencies of circulating CD8+ T-cells that recognise defined viral peptides are maintained for years, and include individual CD8+ clones that have undergone extensive clonal expansion and phenotypic diversification in vivo. Following stem cell transplantation, the kinetics of HCMV-specific CD8+ T-cell reconstitution in the recipient are related to the presence or absence of antigen-experienced CD8+ T-cells transferred via the allograft, and to the presence of the virus in the recipient. We discuss recent progress in our understanding of HCMV-specific immunity in healthy virus carriers and in recipients after alloSCT.

T cell dynamics in HIV-1 infection

In the absence of antiretroviral treatment, HIV-1 establishes a chronic, progressive infection of the human immune system that invariably, over the course of years, leads to its destruction and fatal immunodeficiency. Paradoxically, while viral replication is extensive throughout the course of infection, deterioration of conventional measures of immunity is slow, including the characteristic loss of CD4(+) T cells that is thought to play a key role in the development of immunodeficiency. This conundrum suggests that CD4(+) T cell-directed viral cytopathicity alone cannot explain the course of disease. Indeed, recent advances now indicate that HIV-1 pathogenesis is likely to result from a complex interplay between the virus and the immune system, particularly the mechanisms responsible for T cell homeostasis and regeneration. We review these data and present a model of HIV-1 pathogenesis in which the protracted loss of CD4(+) T cells results from early viral destruction of selected memory T cell populations, followed by a combination of profound increases in overall memory T cell turnover, damage to the thymus and other lymphoid tissues, and physiological limitations in peripheral CD4(+) T cell renewal.

Homeostatic control of T-cell generation in neonates

T cells are produced through 2 mechanisms, thymopoiesis and proliferative expansion of postthymic T cells. Thymic output generates diversity of the pool, and proliferation achieves optimal clonal size of each individual T cell. To determine the contribution of these 2 mechanisms to the formation of the initial T-cell repertoire, we examined neonates of 30 to 40 weeks' gestation. Peripheral T cells were in a state of high proliferative turnover. In premature infants, 10% of T cells were dividing; the proliferation rates then declined but were still elevated in mature newborns. Throughout the third trimester, concentrations of T-cell-receptor excision circles (TRECs) were 10 per 100 T cells. Stability of TREC frequencies throughout the period of repertoire generation suggested strict regulation of clonal size to approximately 10 to 20 cells. Neonatal naive CD4+ and CD8+ T cells were explicitly responsive to IL-7; growth-promoting properties of IL-15 were selective for newborn CD8+ T cells. Neonatal T cells expressed telomerase and, in spite of the high turnover, built up a telomeric reserve. Thus, proliferative expansion, facilitated by increased cytokine responsiveness, and thymopoiesis complement each other as mechanisms of T-cell production in neonates. Maintaining optimal clonal size instead of filling the space in a lymphopenic host appears to regulate homeostatic T-cell proliferation during fetal development.

Long-term immune dysfunction after radiotherapy to the head and neck area

BACKGROUND

Hematological side effects are not generally expected due to radiotherapy involving limited radiation fields; however, patients with squamous cell carcinoma of the head and neck (SCCH and N) receiving radiation therapy frequently have chronic intraoral infections. Xerostomia has been implicated as a cause of it, but local or systemic immune alterations are not usually considered.

METHODS

With the purpose of evaluating the impact of radiotherapy treatment to different anatomic sites on immune function, 70 patients were evaluated during and after radiotherapy: 50 cases with SCCH and N, 10 with squamous cell carcinoma of the uterine cervix (SCCUC) and 10 patients with central nervous system tumors (CNS). We analyzed lymphocyte counts and T-cell subsets, and over time, their association with the presence of intracellular infections and disease-free survival.

RESULTS

Severe lymphopenia was observed in patients with SCCUC and SCCH and N by the fifth week of treatment. Patients with CNS tumors developed mild lymphopenia. In patients with SCCH and N and UC, lower counts were seen in B cells and total T lymphocyte counts including both CD4(+) and CD8(+) cell subsets. The patients with SCCUC recovered lymphocyte counts by the 24th month but T-cell subsets lagged behind. None of the SCCH and N patients had fully recovered by 60 months of follow-up. Recurrence correlates with low lymphocyte counts.

DISCUSSION

This work highlights the vulnerability of the head and neck area to the impact of radiotherapy as a reservoir of lymphoid cells. The possibility of recovery as a consequence of thymopoiesis and/or peripheral clonal expansion may limit the antigen-specific recognition of relevant tumor or microbial antigens and cause significant and prolonged immune alterations that may impact long-term survival.

Early host CD8 T-cell recovery and sensitized anti-donor interleukin-2-producing and cytotoxic T-cell responses associated with marrow graft rejection following nonmyeloablative allogeneic bone marrow transplantation

OBJECTIVE

We developed a nonmyeloablative conditioning regimen for allogeneic bone marrow transplantation (BMT) followed by donor lymphocyte infusions (DLI) for treatment of chemotherapy refractory malignancies. Although the majority of patients who receive this regimen achieve lasting mixed or full allogeneic chimerism, approximately 30% show initial mixed chimerism followed by loss of the donor graft. These patients recover host hematopoiesis without significant cytopenias. To assess the role of immunologic rejection in graft loss, we compared T-cell recovery and in vitro alloresponses in six patients who lost their marrow graft to that in 16 concurrent patients with sustained donor chimerism.

PATIENTS AND METHODS

Conditioning included pretransplant cyclophosphamide (150-200 mg/kg), thymic irradiation (700 cGy), and pre- and post-transplant equine antithymocyte globulin (ATG; ATGAM). HLA-identical related donor BMT was followed by DLI at approximately day 35 in patients without graft-vs-host disease.

RESULTS

The group with transient chimerism showed significantly increased circulating host T-cell (median 416 cells/mm(3) vs 10 cells/mm(3), p<0.05) and CD8 T-cell numbers (354 cells/mm(3) vs 71 cells/mm(3), p<0.05) compared to the group with stable mixed or full donor chimerism within the first 100 days post-BMT. All DLI recipients who lost chimerism following DLI had greater than 80% recipient T cells at the time of DLI, whereas those with persistent chimerism had <60% host T cells. Graft rejection was associated with the development of a sensitized anti-donor bulk cytotoxic T-lymphocyte (CTL) response in 4 of 6 evaluated patients, compared to only 1 of 10 evaluated patients with sustained chimerism (p<0.05). Additionally, 3 of 5 evaluated transient chimeras showed high anti-donor CTL precursor frequencies in limiting dilution assays, and 3 of 4 evaluated transient chimeras showed high anti-donor interleukin-2 (IL-2)-producing T-helper (T(H)) cell frequencies. High anti-donor T(H) or cytotoxic T-lymphocyte precursors were not detected in sustained chimeras.

CONCLUSION

These data indicate that loss of chimerism in patients receiving this nonmyeloablative regimen is due to immune-mediated rejection. This rejection appears to bemediated by recovering recipient cytolytic CD8(+) cells as well as IL-2-producing recipient T(H) cells. These data are the first to demonstrate sensitization of recipient anti-donor IL-2-producing cells in association with human marrow allograft rejection.

Cellular and humoral immune reconstitution after autologous peripheral blood stem cell transplantation (PBSCT)

Immune reconstitution after autologous peripheral blood stem cell transplantation (PBSCT) is of particular interest because of its importance for clinical outcome. Despite prolonged immunosuppression, especially of CD4(+) cells, few infections after neutrophil recovery occur. Only reactivation of varicella zoster virus (VZV) is more frequent in the first year after transplantation. From August 1997 to May 2001, we prospectively evaluated 38 patients prior to conditioning and during follow-up of 12 months post-transplant for virus antibodies [measles, mumps, rubella, polio, herpes simplex, varicella zoster, mononucleosis, cytomegalovirus (CMV)] and lymphocyte subpopulations by flow cytometry. CD3(+) T lymphocytes, CD8(+) T cells, and B-lymphocyte reconstitution in our study confirms previous reports. Complete CD4(+) lymphocyte reconstitution was not achieved in the 12 months post-transplant leading to a suppressed CD4/CD8 ratio. IgG antibody titers against measles, mumps, rubella, and polio were present in almost all patients pretransplant and during 12 months post-transplant, indicating persistent humoral immunity. CD3(+) and CD8(+) counts of patients with clinical VZV reactivation ( n=5) post-transplant were significantly higher (median: 1201/microl and 938/microl, respectively) than in patients without VZV reactivation (median: 594/microl and 482/microl, respectively) 6-12 months post-transplant. Positive CMV titers pretransplant ( n=19) were also correlated with higher CD3(+) and CD8(+) counts 3-6 months post-transplant (median: 1050/microl and 1056/microl, respectively) compared to CMV-negative patients (738/microl and 584/microl, respectively), although none of the patients suffered from CMV disease. Therefore, we conclude that persistent viral infections can contribute to the CD8(+) T-cell reconstitution after PBSCT by oligoclonal expansion of antigen-specific memory CD8(+) T cells.

Quantification and cytokine production of circulating lymphoid and myeloid cells in acute myelogenous leukaemia

A simple assay was developed to assess the potential of patients with acute myelogenous leukaemia (AML) to respond to immunotherapy. Lymphocytes, monocytes and leukaemic blasts with their corresponding intracellular cytokine profiles were evaluated by four-colour flow cytometry. In 50 microl samples of whole blood, surface labelling for CD45, CD8 and CD3 was used for cell identification prior to intracellular staining for interleukin (IL)-4, IL-10, IL-12 and interferon (IFN)-gamma. Absolute numbers of CD8(+) and CD8(-) (putative CD4(+)) T-cells, NK cells (CD8(+)/CD3(-)) and monocytes were determined by reference to a fixed number of added fluorescent beads. The absolute numbers of CD8(-) and CD8(+) T-cells in the blood of patients with AML were similar to those of normal controls. More of the lymphocytes in the blood of leukaemic patients spontaneously produced cytokines compared with those of controls. Furthermore, primary AML blasts secreted predominantly IFN-gamma. After recovery from chemotherapy, lymphocyte counts tended to be lower than in normals and reduction of NK cells reached significance after the second chemotherapy (P=0.01). A prominent CD8(lo)/CD3(lo-int) lymphocyte subset appeared after recovery in some patients. This laboratory application of the study of cell subsets and intracellular cytokines in patients undergoing treatment may be helpful in monitoring immunological responses in AML.

Rapid immune reconstitution following autologous hematopoietic stem cell transplantation in children: a single institution experience

In this retrospective study, we review the immune reconstitution of children undergoing autologous hematopoietic stem cell transplantation. A total of 125 patients underwent autologous transplantation between 1992 and 2000. The report includes data on 58 patients. Data were not available on the remaining patients who either died before testing or data were not obtained. The parameters evaluated include: (a) immunophenotype by flow cytometry to quantify lymphocyte subpopulations (b) mitogen stimulation assays, and (c) quantitative immunoglobulins. The analysis reveals that CD3+ cells did not reach the normal range during the first year post-transplant. The median percentage of CD4+ cells was below normal up to 6 months post-transplant, while the absolute number remain low throughout the first year. The CD8+ percentage and absolute numbers remain normal at all times post-transplant. The CD19+ cells were also normal post-transplantation. The mitogen lymphocyte stimulation was normal in 27 out of 31 patients tested after 6 months post-transplant. Our analysis of immune reconstitution shows a similar pattern to previous studies with a faster recovery of the CD4/CD8 ratio, especially in those patients who did not receive TBI. In conclusion, the observed deficiencies are transient and have very little clinical significance because, historically, the rate of serious infections is low despite prolonged immune suppression. The recovery post-autologous transplant is fast.

Cytotoxic chemotherapy preceding apheresis of peripheral blood progenitor cells can affect the early reconstitution phase of naive T cells after autologous transplantation

Transient T cell immunodeficiency is a common complication following hematopoietic stem cell transplantation. In breast cancer patients transplanted with autologous peripheral blood progenitor cells (PBPC) harvested after cytotoxic treatment with either cyclophosphamide or epirubicin plus paclitaxel, we evaluated T cells infused in grafts and in peripheral blood during the early reconstitution phase. We found that PBPC grafts harvested after treatment with epirubicin plus paclitaxel contained substantially larger numbers of T cells with less altered composition than after cyclophosphamide. Three months after high-dose cytotoxic chemotherapy, the numbers and the kinetics of circulating naive T cells, but not of memory and CD28- T cells, correlated positively with the number of naive T cells infused PBPC grafts. Finally, retrospective analysis of two cohorts of patients transplanted in different clinical settings with PBPC grafts harvested following cyclophosphamide or epirubicin plus paclitaxel showed apparently different susceptibilities to develop endogenous varicella zoster virus reactivation in the first year after high-dose cytotoxic chemotherapy. On the whole, these data indicate that number and composition of T cells in PBPC grafts vary according to the former cytotoxic therapy, and suggest that autologous transfer of T cells may accelerate the early T cell reconstitution phase and possibly ameliorate immune competence in patients rendered lymphopenic by high-dose chemotherapy.

The hematologist and radiation casualties

Since the terrorist attack of September 11, 2001, preparation by the health care system for an act of terrorism has been mandated by leaders of governments. Scenarios for terrorist acts involving radioactive material have been identified, and approaches to management (based on past experience from atomic weapons detonations and radiation accidents) have been developed. Because of their experience in managing patients with profound cytopenia and/or marrow aplasia, hematologists will be asked to play a significant role in evaluating and treating victims of mass accidental or deliberate exposure to radiation. This review provides a framework for understanding how radiation levels are quantified, how radiation alters the function of hematopoietic (and nonhematopoietic) cells and tissues, and how victims receiving a significant radiation dose can be identified and managed. In Section I, Dr. Nicholas Dainiak reviews four components of the Acute Radiation Syndrome: the hematopoietic, neurovascular, gastrointestinal and cutaneous subsyndromes. Clinical signs and symptoms are discussed for exposed individuals at the time of initial presentation (the prodromal phase) and during their course of disease (the manifest illness). In Section II, he presents clinical and laboratory methods to assess radiation doses, including time to onset and severity of vomiting, rate of decline in absolute blood lymphocyte count and the appearance of chromosome aberrations such as dicentrics and ring forms. Potential scenarios of a radiation terrorist event are reviewed, and methods for initial clinical assessment, triage, and early management of the acute radiation syndrome and its component subsyndromes are summarized. In Section III, Dr. Jamie Waselenko reviews the hematopoietic syndrome, and presents guidelines for the use of cytokine therapy, antibiotics, and supportive care that have been developed by the Strategic National Pharmaceutical Stockpile Working Group. Results of preclinical and clinical growth factor therapy studies with G-CSF, GM-CSF, pegylated G-CSF, SCF, and IL-3 are summarized. When and how potassium iodide should be used after exposure to radioiodines is also reviewed. In Section IV, Dr. James Armitage describes a narrow "window" of 7 to 10 Gy where therapy with stem cell transplantation may be appropriate. Victims who are candidates for allotransplantation should not have major trauma or significant injury to other (nonhematopoietic) tissues. Rarely, victims may have an identical sibling or autologous stored marrow or blood stem cells, in which case the threshold for transplantation is 4 Gy. In Section V, Dr. Thomas MacVittie describes new directions for therapy, using cytokines such as IL-7, keratinocyte growth factor, and FLT-3. The potential for combinations of cytokines to enhance hematopoietic recovery is also reviewed.

CD57+ T cells augment IFN-gamma production in a one-way mixed lymphocyte reaction and their expansion after stem cell transplantation in paediatric patients

To clarify the immune response of CD57+ T cells (most of them are CD8+) in peripheral blood (PB) against alloantigens in order to elucidate the T helper 1 (Th 1) immune response, we assessed the role of CD57+ T cells in IFN-gamma (one of the representative Th 1 cytokines) production in a one-way mixed lymphocyte reaction (MLR). In this study, we showed that CD57+ T cells in responder cells were essential for effective IFN-gamma production in allogeneic MLR due partly to the augmentation of the alloresponse of regular T cells. Furthermore, IFN-gamma production in MLR correlated with the proportions of CD57+ T cells in PB regardless of the responders' age. We also showed that the extent of the expansion of CD57+ T cells in paediatric patients after haematopoietic stem cell transplantation (HSCT) was markedly lower than that in adult patients. In addition, CD57+ T cells purified and activated with a combination of cytokines showed a greater cytotoxicity than regular T cells against human umbilical vein endothelial cells. Because IFN-gamma production in one-way MLR is a useful predictor of graft-versus-host disease (GVHD), especially in the acute phase that occurs after allogeneic HSCT, our findings suggested that CD57+ T cells play a role in the development of GVHD and thus may explain the reason as to why a higher donor age is associated with an increased risk of developing GVHD while, in addition, the incidence of severe GVHD in paediatric patients is lower than that in adult patients.

Decreased levels of recent thymic emigrants in peripheral blood of simian immunodeficiency virus-infected macaques correlate with alterations within the thymus

The thymus is responsible for de novo production of CD4(+) and CD8(+) T cells and therefore is essential for T-cell renewal. The goal of this study was to assess the impact of simian immunodeficiency virus (SIV) infection on the production of T cells by the thymus. Levels of recent thymic emigrants within the peripheral blood were assessed through quantification of macaque T-cell receptor excision circles (TREC). Comparison of SIV-infected macaques (n = 15) to uninfected macaques (n = 23) revealed stable or increased TREC levels at 20 to 34 weeks postinfection. Further assessment of SIV-infected macaques (n = 4) determined that TREC levels decreased between 24 and 48 weeks postinfection. Through the assessment of longitudinal time points in three additional SIVmac239-infected macaques, the SIV infection was divided into two distinct phases. During phase 1 (16 to 30 weeks), TREC levels remained stable or increased within both the CD4 and CD8 T-cell populations. During phase 2 (after 16 to 30 weeks), TREC levels declined in both T-cell populations. As has been described for human immunodeficiency virus (HIV)-infected patients, this decline in TREC levels did at times correlate with an increased level of T-cell proliferation (Ki67(+) cells). However, not all TREC decreases could be attributed to increased T-cell proliferation. Further evidence for thymic dysfunction was observed directly in a SIVmac239-infected macaque that succumbed to simian AIDS at 65 weeks postinfection. The thymus of this macaque contained an increased number of memory/effector CD8(+) T cells and an increased level of apoptotic cells. In summary, reduced levels of TREC can be observed beginning at 16 to 30 weeks post-SIV infection and correlate with changes indicative of dysfunction within the thymic tissue. SIV infection of macaques will be a useful model system to elucidate the mechanisms responsible for the thymic dysfunction observed in HIV-infected patients.

Delayed type hypersensitivity response to recall antigens does not accurately reflect immune competence in advanced stage breast cancer patients

The development of delayed-type hypersensitivity (DTH) response to recall antigens has long been utilized as a measure of immune competence. It is assumed that because patients with advanced stage cancers exhibit multiple immune system defects they may not be responsive to immunization. We pre-selected patients with advanced HER-2/neu (HER2) overexpressing breast and ovarian cancers for enrolment into a phase I trial designed to evaluate the immunogenicity of a HER2 peptide vaccine based on the patient's immune competence as assessed by DTH skin testing to common recall antigens (Multitest CMI, Institut Merieux, Lyon, France). At the time of a positive DTH response to tetanus toxoid (tt) peripheral blood was obtained to measure T cell responses to tt. Of 53 patients evaluated, 38 (72%) were not anergic. Among the 15 (28%) who were, seven patients with advanced stage breast cancer were re-tested a median of 26 days (range 12-150 days) after receiving a tt bopster vaccination. Five of the seven had positive DTH responses when re-challenged with tt and six had peripheral blood tetanus specific T cell response with stimulation index >2.0. Thus, the majority of patients studied with advanced stage breast or ovarian cancer were able to mount a DTH response to common recall antigens. Moreover, a negative response by DTH testing to a battery of common recall antigens was not a reflection of the breast cancer patient's ability to mount a cell-mediated immune response to a vaccinated antigen, tt.

Defective T-helper cell function after T-cell-depleting therapy affecting naive and memory populations

Impaired T-cell function after T-cell- depleting (TCD) therapy has been hypothesized to be related to a transient predominance of extrathymically expanding memory T cells. To test whether after TCD therapy the naive T-helper cell population is functionally intact, the in vitro immune response of CD4(+)CD45RA(+) (naive) and of CD4(+)CD45RA(-) (memory) cells to polyclonal mitogens (immobilized anti-CD3, phytohemagglutinin) was analyzed by flow cytometry in 22 pediatric patients after high-dose chemotherapy (including 5 after autologous and 5 after allogeneic stem cell support). At 1 to 3 months after TCD therapy, patient samples showing decreased lymphoproliferative responses also showed a reduced induction of the early activation marker CD69 by CD4(+) T cells from 4 to 72 hours after stimulation even when supplemented with exogenous interleukin-2. This defect affected CD4(+)CD45RA(-) cells, but, strikingly, also CD4(+)CD45RA(+) cells, including samples in which CD4(+)CD45RA(+) cells were more than 90/microL, thus indicating ongoing thymopoiesis. Histogram analyses showed the median peak channel of CD69 in control CD4(+)CD45RA(+) cells rising 98-fold (median) but only 28-fold in patient cells (P <.0001). Apoptosis as detected by annexin V staining was increased in resting patient CD4(+) T cells (25% versus 6%) and also affected CD4(+)CD45RA(+) cells (12% versus 5%, P <.01). When peripheral blood mononuclear cells (PBMCs) were enriched for T cells, stimulatory responses of CD4(+) cells and of CD4(+)CD45RA(+) cells markedly improved. Thus, after TCD therapy suppressor factors contained in the non-T-cell fraction of PBMCs may affect T-helper cells irrespective of their naive or memory phenotype thus extending T-cell dysfunction to the presumably thymus-dependently regenerated T cells.

Current chemotherapy protocols for childhood acute lymphoblastic leukemia induce loss of humoral immunity to viral vaccination antigens

OBJECTIVE

To evaluate viral vaccination immunity and booster responses in children treated successfully for acute lymphoblastic leukemia by chemotherapy and to study the response to treatment of antibody-producing plasma cells that are important for persistence of humoral immunity.

METHODS

Forty-three children who were in continuous first remission for a median of 5 years (range: 2-12 years) were studied. Before the leukemia was diagnosed, all children had been immunized against measles, mumps, and rubella according to the Swedish National immunization program. We analyzed levels of serum antibodies against measles and rubella by enzyme immunoassays. Avidity tests for measles antibodies were concomitantly performed by enzyme-linked immunosorbent assay for measles virus immunoglobulin G detection. The proportion of plasma cells in bone marrow was studied by flow cytometry at different times during treatment and follow-up. Children who lacked protective levels of antibodies to vaccination antigens were reimmunized. Serum was collected 3 months after immunization to assess vaccination responses.

RESULTS

After completion of the treatment, only 26 of the 43 children (60%) were found to be immune against measles and 31 (72%) against rubella. The proportion of bone marrow plasma cells decreased during treatment but returned to normal after 6 months. Revaccination caused both primary and secondary immune responses. Six of the 14 children without immunity failed to achieve protective levels of specific antibodies against measles and 3 against rubella.

CONCLUSIONS

Our finding of loss of antibodies against measles and rubella in children treated with intensive chemotherapy suggests that reimmunization of these patients is necessary after completion of the treatment. To determine reimmunization schedules for children treated with chemotherapy, vaccination responses need to be studied further.

Increased thymic mass and circulating naive CD4 T cells in HIV-1-infected adults treated with growth hormone

OBJECTIVE

To determine whether treatment with growth hormone (GH) enhances thymopoiesis in individuals infected with HIV-1.

METHODS

Five HIV-1-infected adults were treated with GH for 6-12 months in a prospective open-label study. Immunological analyses were performed before GH treatment and repeated at 3 month intervals after GH initiation. Thymic mass was analysed using computed tomography with quantitative density and volume analysis. Analysis of circulating lymphocytes, including naive and memory T cell subsets, was performed using multiparameter flow cytometry.

RESULTS

GH treatment was associated with a marked increase in thymic mass in all GH recipients. Circulating naive CD4 T cells also increased significantly in all patients during GH therapy, suggesting an enhancement of thymopoiesis.

CONCLUSION

GH has significant effects on the human immune system, including the reversal of thymic atrophy in HIV-1-infected adults. De-novo T cell production may thus be inducible in immunodeficient adults.

T-cell dynamics after high-dose chemotherapy in adults: elucidation of the elusive CD8+ subset reveals multiple homeostatic T-cell compartments with distinct implications for immune competence

Recovery of total T cell numbers after in vivo T-cell depletion in humans is accompanied by complex perturbation within the CD8+ subset. We aimed to elucidate the reconstitution of CD8+ T cells by separate analysis of putative naïve CD95- CD28+, memory CD95+ CD28+ and CD28- T cell compartments after acute maximal depletion by high-dose chemotherapy (HD-ChT) in women with high-risk breast cancer. We found that recovery of putative naïve CD8+ CD95- CD28+ and CD4+ CD95- CD28+ T cells, was compatible with a thymus-dependent regenerative pathway since their recovery was slow and time-dependent, their values were tightly related to each other, and their reconstitution patterns were inversely related to age. By analysing non-naïve T cells, a striking diversion between putative memory T cells and CD28- T cells was found. These latter increased early well beyond normal values, thus playing a pivotal role in total T-cell homeostasis, and contributed to reduce the CD4 : CD8 ratio. In contrast, putative memory T cells returned to values not significantly different from those seen in patients at diagnosis, indicating that this compartment may recover after HD-ChT. At 3-5 years after treatment, naïve T cells persisted at low levels, with expansion of CD28- T cells, suggesting that such alterations may extend further. These findings indicate that CD28- T cells were responsible for 'blind' T-cell homeostasis, but support the notion that memory and naïve T cells are regulated separately. Given their distinct dynamics, quantitative evaluation of T-cell pools in patients undergoing chemotherapy should take into account separate analysis of naïve, memory and CD28- T cells.

Immune reconstitution in patients with HIV infection

The peripheral T cell pool is damaged by HIV-1 infection and can be regenerated by production of new T lymphocytes either from the thymus or from proliferation of post-thymic T cells. A critical question for AIDS patients is whether treatment with antiretroviral drugs can restore the capability to produce new T lymphocytes. The development of a new assay of thymus function in adults (the measurement of T cell receptor excision circles, TRECs), and studies of thymus biopsies in untreated and treated HIV-1-infected patients, have suggested that in select patients the thymus can regenerate on antiretroviral therapy. New strategies to overcome the thymic atrophy of aging are needed to improve thymic function in the majority of AIDS patients.

Hematopoietic cellular therapy: implications for the flow cytometry laboratory

Advances in hematopoietic stem cell transplantation, gene therapy, and immunotherapy have necessitated a host of novel monitoring procedures. Cell sorting is also coming of age as a clinical procedure designed to organize hematopoietic grafts for specificity of cellular components designed for individual patients or diseases. This article has focused on these novel developments in their historical context. The next generation of transplantation flow cytometry promises to be an exciting one.

Impact of high-dose chemotherapy on antigen-specific T cell immunity in breast cancer patients. Application of new flow cytometric method

The present study analyses the influence of high-dose chemotherapy (HD) and autologous stem cell transplantation on natural and vaccine-induced specific immunity in breast cancer patients. Peripheral blood was collected from five breast cancer patients at serial time points in connection with treatment and in a follow-up period of 1 year. The frequencies of CD8+ and CD4+ T cells responsive to cytomegalovirus (CMV), varicella zoster virus (VZV), and tetanus in antigen-activated whole blood were determined by flow cytometric analysis of CD69, TNF alpha, IFN gamma and IL-4 expression. Mononuclear cells were labelled with PKH26 dye and the CMV, VZV, and tetanus toxoid-specific proliferation of T cell subpopulations was analysed by flow cytometry. In none of the patients did the treatment result in loss of overall T cell reactivity for any of the antigens. Prior to chemotherapy 5/5 patients possessed TNF alpha expressing T cells specific for CMV, 4/5 for VZV, and 3/5 for tetanus. One year after stem cell transplantation all patients possessed TNF alpha expressing T cells specific for CMV, VZV and tetanus. The highest percentages of cytokine-responding T cells were seen after stimulation with CMV antigen. In general, the lowest reactivity (close to zero) was measured in G-CSF-mobilised blood at the time of leukapheresis. In spite of a continuously reduced CD4 to CD8 ratio after transplantation, recovery of CD4+ T cells usually occurred prior to CD8+ recovery and often to a higher level. The study demonstrates that natural as well as vaccine-induced specific immunity established prior to HD can be regained after stem cell transplantation. These data indicate that introduction of a preventive cancer vaccination in combination with intensive chemotherapy may be a realistic treatment option.

Effects of combination chemotherapy and highly active antiretroviral therapy on immune parameters in HIV-1 associated lymphoma

OBJECTIVE

To measure the effects of combined chemotherapy and highly active antiretroviral therapy (HAART) on immune cell counts and plasma HIV-1 RNA loads in patients with AIDS-related lymphoma (ARL) to determine the implications for opportunistic infection prophylaxis and medium-term immune function.

DESIGN AND METHODS

Peripheral blood total lymphocyte count, CD4 T-cell count, CD8 T-cell count, CD19 B-cell count, CD16/CD56 natural killer cell count and plasma HIV-1 RNA load were prospectively measured at ARL diagnosis, at 1 and 3 months during and 1, 3 and 6 months after chemotherapy in twenty patients receiving HAART.

RESULTS

Significant declines in T-helper cell (CD4) count, natural killer cell (CD16/CD56) and B lymphocyte count (CD19 cells) occurred during the first 3 months of chemotherapy. There was no significant alteration in the T-cytotoxic cell (CD8) count, CD4 percentage or HIV-1 RNA load during the study period. The T-helper cell and natural killer cell counts recovered to pre-treatment levels within 1 month of finishing chemotherapy. The recovery of B-cells was slower with pre-treatment levels only being achieved after 3 months. The recovery of CD4 T-cell count following completion of chemotherapy was more rapid than described for ARL patients who were not receiving concomitant HAART.

CONCLUSIONS

By combining chemotherapy with HAART, immune function is better maintained in the medium term. The CD4 T-cell count falls by 50% during chemotherapy and this will help to identify patients who require opportunistic infection prophylaxis during chemotherapy.

Alterations in thymopoiesis in intact and peripubertally orchidectomized adult rats of different age

In adult rats 3, 6 and 9 months post-orchidectomy performed at the age of 30 days the thymus weight, thymocyte yield and relative proportions of thymocyte subsets (delineated by expression of CD4/CD8 molecules and TCRalphabeta) were analyzed in order to elucidate a putative role of male gonadal hormones in the shaping of thymus size and intrathymic T cell maturation. In 4-month-old control rats the thymus size and cellularity returned to the corresponding levels in 1-month-old rats. These levels were sustained during the following 6 months. In spite of that, the distribution of the main thymocyte subsets in these rats was subjected to significant changes, probably due to an age-associated diminishing thymus ability to provide efficient T cell differentiation. The results added further weight to a potential feedback regulatory role of CD4+8- cells in thymopoiesis. Furthermore, they revealed that the orchidectomy-induced (i) enlargement of the thymus size and enrichment of the thymic lymphoid cell content are of a limited duration; and (ii) alterations in the relative proportion of thymocytes become quantitatively more pronounced with duration of the gonadal deprivation. Thus, the study also indicates that the age-associated changes in gonadal hormones may be, at least partly, responsible for the age-related reshaping of the T cell maturation sequence, and hence for remodeling T cell dependent immune functions.

CD8+CD28- T cells: certainties and uncertainties of a prevalent human T-cell subset

Human peripheral blood CD8+ T cells comprise cells that are in different states of differentiation and under the control of complex homeostatic processes. In a number of situations ranging from chronic inflammatory conditions and infectious diseases to ageing, immunodeficiency, iron overload and heavy alcohol intake, major phenotypic changes, usually associated with an increase in CD8+ T cells lacking CD28 expression, take place. CD8+CD28- T cells are characterized by a low proliferative capacity to conventional stimulation in vitro and by morphological and functional features of activated/memory T cells. Although the nature of the signals that give origin to this T-cell subset is uncertain, growing evidence argues for the existence of an interplay between epithelial cells, molecules with the MHC-class I fold and CD8+ T cells. The possibility that the generation of CD8+CD28- T cells is the combination of TCR/CD3zeta- and regulatory factor-mediated signals as a result of the sensing of modifications of the internal environment is discussed.

Leridistim, a chimeric dual G-CSF and IL-3 receptor agonist, enhances multilineage hematopoietic recovery in a nonhuman primate model of radiation-induced myelosuppression: effect of schedule, dose, and route of administration

Leridistim is from the myelopoietin family of proteins, which are dual receptor agonists of the human interleukin-3 and G-CSF receptor complexes. This study investigated the effect of dosage, administration route, and schedule of leridistim to stimulate multilineage hematopoietic recovery in total body irradiated rhesus monkeys. Animals were x-irradiated on day 0 (600 cGy, 250 kVp) and then received, on day 1, leridistim s.c. in an abbreviated, every-other-day schedule at 200 microg/kg, or daily at 50 microg/kg, or i.v. daily or every-other-day schedules at 200 microg/kg dose. Other cohorts received G-CSF (Neupogen((R)) [Filgrastim]) in an every-other-day schedule at 100 microg/kg/day, or autologous serum (0.1%) s.c. daily. Hematopoietic recovery was assessed by bone marrow clonogenic activity, peripheral blood cell nadirs, duration of cytopenias, time to recovery to cellular thresholds, and requirements for clinical support. Leridistim, administered s.c. every other day, or i.v. daily, significantly improved neutrophil, platelet, and lymphocyte nadirs, shortened the respective durations of cytopenia, hastened trilineage hematopoietic recovery, and reduced antibiotic and transfusion requirements. A lower dose of leridistim administered daily s.c. enhanced recovery of neutrophil and platelet parameters but did not affect lymphocyte recovery relative to controls. Leridistim, a novel engineered hematopoietic growth factor administered at the appropriate dose, route and schedule, stimulates multilineage hematopoietic reconstitution in radiation-myelosuppressed nonhuman primates.

Immunity of patients surviving 20 to 30 years after allogeneic or syngeneic bone marrow transplantation

The duration of immunodeficiency following marrow transplantation is not known. Questionnaires were used to study the infection rates in 72 patients surviving 20 to 30 years after marrow grafting. Furthermore, in 33 of the 72 patients and in 16 donors (siblings who originally donated the marrow) leukocyte subsets were assessed by flow cytometry. T-cell receptor excision circles (TRECs), markers of T cells generated de novo, were quantitated by real-time polymerase chain reaction. Immunoglobulin G(2) (IgG(2)) and antigen-specific IgG levels were determined by enzyme-linked immunosorbent assay. Infections diagnosed more than [corrected] 15 years after transplantation occurred rarely. The average rate was 0.07 infections per patient-year (one infection every 14 years), excluding respiratory tract infections, gastroenteritis, lip sores, and hepatitis C. The counts of circulating monocytes, natural killer cells, B cells, CD4 T cells, and CD8 T cells in the patients were not lower than in the donors. The counts of TREC(+) CD4 T cells in transplant recipients younger than age 18 years (at the time of transplantation) were not different from the counts in their donors. In contrast, the counts of TREC(+) CD4 T cells were lower in transplant recipients age 18 years or older, even in those with no history of clinical extensive chronic graft-versus-host disease, compared with their donors. The levels of total IgG(2) and specific IgG against Haemophilus influenzae and Streptococcus pneumoniae were similar in patients and donors. Overall, the immunity of patients surviving 20 to 30 years after transplantation is normal or near normal. Patients who received transplants in adulthood have a clinically insignificant deficiency of de novo-generated CD4 T cells, suggesting that in these patients the posttransplantation thymic insufficiency may not be fully reversible.

Therapeutic immune reconstitution in HIV-1-infected children is independent of their age and pretreatment immune status

OBJECTIVE

To evaluate long-term immune reconstitution of children treated with highly active antiretroviral therapy (HAART).

METHODS

The long-term immunological response to HAART was studied in 71 HIV-1-infected children (aged 1 month to 18 years) in two prospective, open, uncontrolled national multicentre studies. Blood samples were taken before and after HAART was initiated, with a follow-up of 96 weeks, and peripheral CD4 and CD8 T cells plus naive and memory subsets were identified in whole blood samples. Relative cell counts were calculated in relation to the median of the age-specific reference.

RESULTS

The absolute CD4 cell count and percentage and the CD4 cell count as a percentage of normal increased significantly (P < 0.001) to medians of 939 x 106 cells/l (range, 10-3520), 32% (range, 1-50) and 84% (range, 1-161), respectively, after 48 weeks. This increase was predominantly owing to naive CD4 T cells. There was a correlation between the increase of absolute naive CD4 T cell counts and age. However, when CD4 T cell restoration was studied as percentage of normal values, the inverse correlation between the increase of naive CD4 T cell count and age was not observed. In addition, no difference in immunological reconstitution was observed at any time point between virological responders and non-responders.

CONCLUSIONS

Normalization of the CD4 cell counts in children treated with HAART is independent of age, indicating that children of all age groups can meet their CD4 T cell production demands. In general, it appears that children restore their CD4 T cell counts better and more rapidly than adults, even in a late stage of HIV-1 infection.

Biological treatment in acute myelogenous leukaemia: how should T-cell targeting immunotherapy be combined with intensive chemotherapy?

T-cell targeting immunotherapy is now considered as a possible strategy in the treatment of acute myelogenous leukaemia (AML). Clinical importance of antileukaemic T-cell reactivity after allogeneic stem cell transplantation (SCT) is well established and the early experience from IL-2 therapy suggests that even autologous T-cells can mediate antileukaemic reactivity. The clinical experience also indicates that immunotherapy should begin when the leukaemia cell burden is minimal, and the detection of an operative cellular immune system, even in patients with chemotherapy-induced cytopenia, further suggests that it is possible to begin T-cell targeting therapy early after chemotherapy while patients are still cytopenic. However, adult patients in particular have a T-cell defect after chemotherapy that may last for several months. For this reason immunotherapy should probably be continued or repeated until a maximal effect is achieved when the patients no longer have a T-cell defect. This treatment approach may also be considered in combination with autologous SCT. T-cell targeting regimens should include, if possible, several therapeutic components. Firstly, native AML blasts can function as accessory cells during T-cell activation and in vivo therapy with T-cell growth factors (e.g., IL-2, IL-15) may then enhance antileukaemic reactivity or non-specific cytotoxicity against the AML cells; and secondly, a further enhancement of AML-specific reactivity may be achieved by vaccination with AML-specific peptides, immunisation with AML-blasts expressing a dendritic cell phenotype, or exposure to normal antigen-presenting cells (APC) pulsed with or expressing AML-specific peptide sequences.

Interleukin-7: master regulator of peripheral T-cell homeostasis?

Recent evidence has implicated interleukin-7 (IL-7) as a master regulator of T-cell homeostasis, based upon its essential role in the homeostatic expansion of naive T-cell populations in response to low-affinity antigens (Ags) and its capacity to enhance dramatically the expansion of peripheral T-cell populations in response to high-affinity Ags. Furthermore, T-cell-depleted humans have a unique inverse relationship between the peripheral CD4(+) T-cell count and the level of circulating IL-7. Together, these data suggest that increased amounts of IL-7 become available following T-cell depletion, thus, enhancing the high- and low-affinity Ag-driven expansion of the population of residual, mature T cells and boosting thymic regenerative capacity, as a means to restore T-cell homeostasis.

Immune reconstitution and production of intracellular cytokines in T lymphocyte populations following autologous peripheral blood stem cell transplantation

For the better understanding of engraftment properties after autologous peripheral blood stem cell transplantation (PBSCT), hematopoietic recovery, immune reconstitution and functional capacity of cytokine production in different lymphocyte populations were examined. In a prospective study, we examined 24 patients suffering from different malignancies after autologous PBSCT. The examination intervals were 1, 3, 6 and 12 months after PBSCT. T cells, B cells and NK cells were analyzed using flow cytometry. The expression and kinetics of cytokines in T lymphocytes were evaluated in 10 patients by intracellular staining of cytokines after PMA/ionomycin stimulation. We observed rapid hematopoietic engraftment proceeding to stable long-term reconstitution. For CD3(+) lymphocytes, a consistent reconstitution associated with an increase in CD3(+)CD8(+) cytotoxic T cells was observed, whereas the CD3(+)CD4(+) helper/inducer T cells remained low (< 200/microl). Impaired B lymphopoiesis with severe depression (<1%) was detected 1 month after PBSCT but recovered thereafter (12.8% after 3 months). The percentages of cytokine-producing T cells and the mean fluorescence intensity (MFI) shifts suggested an insufficient capacity for producing IFNgamma, in particular for CD3(+)CD4(+) T cells, compared to healthy volunteers early after PBSCT. Rapid hematopoietic recovery and partly impaired immune reconstitution, especially regarding the regeneration of B lymphocytes and T helper cells, was observed. The CD4(+) subpopulation remained low throughout the period of examination, whereas the B cells showed a delayed recovery after 3 months. Cytokine production proved to be sufficient after in vitro stimulation in T cell populations with the exception of IFNgamma synthesis.

Selective increases in HIV-specific neutralizing antibody and partial reconstitution of cellular immune responses during prolonged, successful drug therapy of HIV infection

Because the immune response to HIV depends on viral gene expression, we examined the HIV-specific immune responses in persons whose viral load after highly active antiretroviral therapy (HAART) was <400 on at least 3 occasions over a 12-month interval. Eleven patients were identified. While there was little change in mean HIV-binding antibody (Ab) titers in this group, two persons mounted increases in HIV envelope-specific binding antibody. Neutralizing antibody (NAb) titers against a panel of HIV-1 primary isolates (BZ167, US1, and CM237) increased post-HAART (80% neutralization titer against US1, p = 0.06; against CM237, p = 0.04). The two persons with large increases in binding antibody also had increases in primary isolate NAb. Roughly half of HAART recipients had significant increases in neutralizing antibody to the primary isolates US1 and CM237. Compared with CD4-matched, non-HAART controls, there were significant increases in NAb against the subtype B primary isolate US1 (p < 0.0009); no increases were seen against more easily neutralized primary isolate BZ167. There were no differences after HAART in antibody-directed cellular cytotoxicity (ADCC). HAART resulted in a partial restoration of lymphoproliferative responses to recall antigens (tetanus and diphtheria). New responses developed to HIV Gag p24. No patient responded to HIV Env gp160 or gp120 either before or after HAART. The data underscore the lack of functional reconstitution of HIV-specific, CD4-mediated responses despite durable suppression of viral replication. In the setting of stable anti-HIV Ab levels, the development of increased NAb in certain individuals suggests that control of the virus by HAART may assist in immune control of HIV.

Immune reconstitution after autologous selected peripheral blood progenitor cell transplantation: comparison of two CD34+ cell-selection systems

BACKGROUND

Selection of CD34+ PBPCs has been applied as a method of reducing graft contamination from neoplastic cells. This procedure seems to delay lymphocyte recovery, while myeloid engraftment is no different from that with unselected PBPC transplants.

STUDY DESIGN AND METHODS

Lymphocyte recovery was studied in two groups of patients who underwent autologous CD34+ PBPC transplant with two different technologies (Ceprate SC, Cellpro [n = 17]; CliniMACS, Miltenyi Biotech [n = 13]). The median number of CD34+ cells transfused was 3.88 x 10(6) per kg and 3.32 x 10(6) per kg, respectively. Residual CD3 cells x 10(6) per kg were 4.97 and 0.58, respectively (p = 0.041). Residual CD19 cells x 10(6) per kg were 1.33 and 0.73, respectively (NS).

RESULTS

No differences were found between the two groups in total lymphocyte recovery to >0.5 x 10(9) per L, which achieved a stable count by Day 30. During the study period, the CD4+ cell count remained below 0.2 x 10(9) per L, and the B-cell subset showed a trend toward normalization. CD3/HLA-DR+ and CD16/56 increased markedly in both groups by Day 30. An increase in CMV (13%) and adenovirus (17.4%) infection was found in both groups.

CONCLUSION

Both CD34+ cell selection technologies used here determined an excellent CD34+ cell purity and an optimal depletion of T cells. The high rate of viral complications is probably due to the inability of residual T cells left from the CD34+ cell selection to generate, immediately after transplant, an adequate number of virus-specific lymphocytes.

The peripheral blood leukocyte phenotype in patients with breast cancer: effect of doxorubicin/paclitaxel combination chemotherapy

Presence of functional immune system is critical for any attempt aimed at improving survival of breast cancer patients by strategies based on immune system manipulation. We evaluated by flow cytometry the phenotype of peripheral blood leukocyte of 43 breast cancer patients. In 11 patients, the phenotype was evaluated before and during the chemotherapy by combination of doxorubicin and paclitaxel (AT). Compared with controls breast cancer patients had significantly higher relative and absolute numbers of CD3 HLA-DR+, CD3+CD69+ and CD14+CD16+, and significantly lower percentages of CD3 and CD8+CD28+ cells. After one cycle of AT, the absolute numbers of CD3 , CD3+CD4+, CD3+CD8+ and CD8+CD28+ cells increased significantly. Present data show a presence of T-cell activation in breast cancer patients. Administration of AT may lead to an increase in functional T-cells in peripheral blood, indicating a potential for combining chemotherapy with immunotherapy in the treatment of breast cancer patients.

CD4 T cell-mediated alloresistance to fully MHC-mismatched allogeneic bone marrow engraftment is dependent on CD40-CD40 ligand interactions, and lasting T cell tolerance is induced by bone marrow transplantation with initial blockade of this pathway

Costimulatory blockade can be used to promote allogeneic marrow engraftment and tolerance induction, but on its own is not 100% reliable. We sought to determine whether one or the other of the CD4 or CD8 T cell subsets of the recipient was primarily responsible for resistance to allogeneic marrow engraftment in mice receiving costimulatory blockade, and to use this information to develop a more reliable, minimal conditioning regimen for induction of mixed chimerism and transplantation tolerance. We demonstrate that a single anti-CD40 ligand mAb treatment is sufficient to completely overcome CD4 cell-mediated resistance to allogeneic marrow engraftment and rapidly induce CD4 cell tolerance, but does not reliably overcome CD8 CTL-mediated alloresistance. The data suggest that costimulation, which activates alloreactive CTL, is insufficient to activate alloreactive CD4 cells when the CD40 pathway is blocked. The addition of host CD8 T cell depletion to anti-CD40 ligand treatment reliably allows the induction of mixed chimerism and donor-specific skin graft tolerance in 3 Gy-irradiated mice receiving fully MHC-mismatched bone marrow grafts. Thus, despite the existence of multiple costimulatory pathways and pathways of APC activation, our studies demonstrate an absolute dependence on CD40-mediated events for CD4 cell-mediated rejection of allogeneic marrow. Exposure to donor bone marrow allows rapid tolerization of alloreactive CD4 cells when the CD40 pathway is blocked, leading to permanent marrow engraftment and intrathymic tolerization of T cells that develop subsequently.

Intact T-cell regenerative capacity in childhood acute lymphoblastic leukemia after remission induction therapy

BACKGROUND

Acute lymphoblastic leukemia (ALL) is a bone marrow disease. This may adversely affect the capacity of T cells to recover from chemotherapy-induced T-cell depletion and thus contribute to the prevailing immune deficiency in ALL patients.

PROCEDURE

We tested the capacity of T-cells to regenerate in 18 ALL children in first clinical remission (median age 4.2 years) at the time of hematologic reconstitution after BFM-ALL induction therapy (treatment-free interval 22 days, median; range 12 to 52 days). All patients had experienced a period of leukopenia (white blood cell count [WBC] <0.95 x 10(9)/l, median) during the final four weeks of induction therapy. T-cells and T-cell subsets were examined by FACS.

RESULTS

At the time of investigation the WBC was near normal (3.5 x 10(9)/l, median). Surprisingly, most cases (78%) showed a complete regeneration of T-cells and its subsets including 1) normal total (CD3+) T-cells (1635/microl, median; range 756-3440/microl); 2) normal T-helper (CD4+) cells (697/microl, median; range 128-1523/microl); and 3) normal T-cytotoxic/suppressor (CD8+) cells (686/microl, median; range 348-1540/microl). Eight patients achieved a normal CD4+/CD8+ ratio (0.8, median). Subset analyses of T-helper cells revealed a normal proportion of CD4+CD45RA+ cells (52%, median) in all but one patient below the age of 6 years, indicating an intact residual thymic activity. No correlation was observed between age at diagnosis and a normal CD4+ count (r = 0.086) or between a normal CD4+ count and a normal proportion of CD4+CD45RA+ cells r = 0.136). A long-term survey in four patients showed altered T-cells after reinduction and during maintenance therapy.

CONCLUSIONS

The findings suggest that ALL per se does not inhibit T-cell regenerative capacity. Thus, the frequently observed longlasting impairment of the T-cell system in ALL is attributable to the treatment rather than to the underlying disease.

Apoptosis in T-lymphocyte subsets in human immunodeficiency virus-infected children measured immediately ex vivo and following in vitro activation

Phosphatidylserine molecules are translocated to the outer plasma membrane of lymphocytes undergoing apoptosis and can be detected by the binding of fluorochrome-conjugated annexin V. Using the annexin V assay, we examined CD4 and CD8 T cells from human immunodeficiency virus (HIV)-infected children for apoptosis upon isolation or following in vitro culture. Immediate ex vivo analysis or overnight culture showed significantly higher levels of apoptosis in CD8 cells than in CD4 cells. Following culture with the activating stimulus phytohemagglutinin or anti-CD3 monoclonal antibody, we observed an increase in the percentage of apoptotic CD4 cells, whereas there was no change in the rate of CD8 cell death. These results demonstrate that in HIV-infected children, CD8 apoptosis may occur at a greater rate than CD4 apoptosis in vivo; greater CD4 depletion may be observed due to more efficient mechanisms for peripheral lymphocyte replacement in the CD8 compartment. Furthermore, our data suggest that CD8 lymphocytes may be maximally activated in vivo, a condition which may lead to the exhaustion of CD8-mediated immunity. These findings clarify the differences between the CD4 and CD8 apoptotic responses to HIV.

Prolonged CD4 depletion after sequential autologous peripheral blood progenitor cell infusions in children and young adults

Administration of mobilized peripheral blood progenitor cells (PBPCs) after high-dose chemotherapy rapidly restores multilineage hematopoiesis, but the ability of such products to restore lymphocyte populations remains unclear. In this report, we evaluated immune reconstitution in a series of patients treated with sequential cycles of high-dose chemotherapy, followed by autologous PBPC infusions (median CD34+ cell dose 7.2 × 106 cells/kg [range 2-29.3]). Although patients experienced rapid reconstitution of B cells and CD8+ T cells, we observed CD4 depletion and diminished immune responsiveness in all patients for several months after completion of therapy. Mature CD4+ T cells contained within the grafts did not appear to contribute substantially to immune reconstitution because CD4 counts did not differ between recipients of unmanipulated T-cell replete infusions versus CD34 selected, T-cell–depleted infusions. Rather, at 12 months after therapy, total CD4 count was inversely proportional to age (ρ = −0.78,P = .04), but showed no relationship to CD34 cell dose (ρ = −0.42, P = .26), suggesting that age-related changes within the host are largely responsible for the limited immune reconstitution observed. These results demonstrate that in the autologous setting, the infusion of large numbers of PBPCs is not sufficient to restore T-cell immune competence and emphasize that specific approaches to enhance immune reconstitution are necessary if immune-based therapy is to be used to eradicate minimal residual disease after autologous PBPC transplantation.

Regulation of extrathymic T cell development and turnover by oncostatin M

Chronic exposure to oncostatin M (OM) has been shown to stimulate extrathymic T cell development. The present work shows that in OM transgenic mice, 1) massive extrathymic T cell development takes place exclusively the lymph nodes (LNs) and not in the bone marrow, liver, intestines, or spleen; and 2) LNs are the sole site where the size of the mature CD4+ and CD8+ T cell pool is increased (6- to 7-fold). Moreover, when injected into OM transgenic mice, both transgenic and nontransgenic CD4+ and CD8+ T cells preferentially migrated to the LNs rather than the spleen. Studies of athymic recipients of fetal liver grafts showed that lymphopoietic pathway modulated by OM was truly thymus independent, and that nontransgenic progenitors could generate extrathymic CD4+CD8+ cells as well as mature T cells under the paracrine influence of OM. The progeny of the thymic-independent differentiation pathway regulated by OM was polyclonal in terms of Vbeta usage, exhibited a phenotype associated with previous TCR ligation, and displayed a rapid turnover rate (5-bromo-2'-deoxyuridine pulse-chase assays). This work suggests that chronic exposure to OM 1) discloses a unique ability of LNs to sustain extrathymic T cell development, and 2) increases the number and/or function of LN niches able to support seeding of recirculating mature T cells. Regulation of the lymphopoietic pathway discovered in OM transgenic mice could be of therapeutic interest for individuals with thymic hypoplasia or deficient peripheral T cell niches.

Recovery of lymphocyte and dendritic cell subsets after autologous CD34+ cell transplantation

Following high-dose chemotherapy (HDC) and peripheral blood progenitor cell transplantation (PBPCT), there are profound changes in leukocyte homeostasis and the immune system is compromised. Transplantation of purified CD34+ cells may further compromise immune recovery because the grafts are depleted of mature immune cells. However, a detailed monitoring of immune cell reconstitution has not been done. We monitored blood levels of antigen-presenting cells (APC) and of lymphocytes by multi-color flow cytometry at different times post CD34+ PBPCT. We found a rapid normalization of circulating levels of the antigen-presenting CD11c+ dendritic cells (defined as lineage- HLA-DR+ CD11c+ cells). There was a slight over-representation of lin- DR+ CD11c- cells at day 42 post transplantation suggesting that the composition of the APC population might be affected. Normal levels of total T, B and NK lymphocytes were rapidly achieved but the composition of the T cell population was abnormal. Patients had elevated levels of CD8+ T cells at early times and a persistent reduction in levels of naive CD8+ T cells (CD8+ CD4- CD45RA+ CD27+) and of naive CD4+ T cells (CD4+CD3+ CD8- CD45RA+). Thus, we found a rapid recovery of DC after CD34+ PBPCT but the specific numerical defects in naive T cells are likely to be a major cause of immune dysfunction in the patients. Bone Marrow Transplantation (2000) 25, 1249-1255.

Assessment of thymic output in adults after haematopoietic stem-cell transplantation and prediction of T-cell reconstitution

BACKGROUND

The potential benefits of haematopoietic stem-cell transplantation are tempered by the depletion of T-cells accompanying this procedure. We used a new technique which quantifies the excisional DNA products of T-cell-receptor (TCR) gene rearrangement to measure thymic output directly in patients with multiple myeloma, and thus assessed the contribution of the thymus to immune recovery after transplantation.

METHODS

We studied 40 patients, 34-66 years of age, who had been randomly assigned myeloablative chemotherapy and autologous peripheral-blood haematopoietic stem-cell transplantation with unmanipulated grafts or grafts enriched for CD34 stem cells. CD4 and CD8 T-cell counts were measured, thymic output was estimated serially until 2 years after transplantation, and percentages of naive T-cells were measured.

FINDINGS

The production of substantial numbers of new naive T cells by the thymus could be detected by 100 days post-transplant; there was a significant inverse relation between age and recovery of new T cells. In the CD34-unselected group, numbers of TCR-rearrangement excision circles returned to baseline after 2 years, whereas in the CD34-selected group, numbers at 2 years were significantly higher than both baseline numbers (p=0.004), and 2-year numbers in the unselected group (p=0.046). Increased thymic output correlated with, and was predictive of, increased naive T-cell numbers and broader T-cell-receptor repertoires.

INTERPRETATION

Our results provide evidence that the adult thymus contributes more substantially to immune reconstitution after haematopoietic stem-cell transplantation than was previously thought, and therefore could be a target for therapeutic intervention.

Shortage of circulating naive CD8+ T cells provides new insights on immunodeficiency in aging

Clinical observations indicate that elderly people are prone to severe, often lethal infectious diseases induced by novel pathogens. Since the ability to mount primary immune responses relies on the availability of naive T cells, the circulating naive T-cell reservoir was evaluated throughout the human life span. Naive T cells were identified as CD95− T lymphocytes for their phenotypic and functional features. Indeed, the lack of CD95 marker is sufficient to identify a population of naive T cells, as defined by coincidence with previously characterized CD45RA+ CD62L+ T cells. Naive CD95− T cells, as expected, require a costimulatory signal, such as CD28, to optimally proliferate after anti-CD3 stimulation. Cytofluorimetric analysis of circulating T lymphocytes from 120 healthy subjects ranging in age from 18 to 105 years revealed that naive T cells decreased sharply with age. The younger subjects had a naive T-lymphocyte count of 825 ± 48 cells/μL, and the centenarians had a naive T-lymphocyte count of 177 ± 28 cells/μL. Surprisingly, the naive T-cell count was lower in CD8+than in CD4+ subsets at any age, and the oldest individuals were almost completely depleted of circulating naive CD8+ T cells (13 ± 4 cells/μL). Concomitantly, a progressive expansion of CD28− T cells occurs with age, which can be interpreted as a compensatory mechanism. These data provide new insights into age-related T-cell–mediated immunodeficiency and reveal some analogies of T-cell dynamics between advanced aging and human immunodeficiency virus (HIV) infection. In conclusion, the exhaustion of the naive CD8+ T-cell reservoir, which has never been reported before, suggests that this T-cell pool is a major target of the aging process and may define a parameter possibly related to the life span of humans.

Reduction of the HIV-1-infected T-cell reservoir by immune activation treatment is dose-dependent and restricted by the potency of antiretroviral drugs

BACKGROUND

Treatments combining T-cell activating agents and potent antiretroviral drugs have been proposed as a possible means of reducing the reservoir of long-lived HIV-1 infected quiescent CD4 T-cells.

OBJECTIVE

To analyse the effect of such therapies on HIV-1 dynamics and T-cell homeostasis.

DESIGN AND METHODS

A mathematical framework describing HIV-1 dynamics and T-cell homeostasis was developed. Three patients who were kept on a particularly potent course of highly active antiretroviral therapy (HAART) were treated with the anti-CD3 monoclonal antibody OKT3 and interleukin (IL)-2. Plasma HIV-RNA, and HIV-RNA and DNA in peripheral blood mononuclear cells and lymph node mononuclear cells were measured. These results and other published studies on the use of IL-2 alone were assessed using our mathematical framework.

RESULTS

We show that outcome of treatment is determined by the relative rates of depletion of the infected quiescent T-cell population by activation and of its replenishment through new infection. Which of these two processes dominates is critically dependent on both the potency of HAART and also the degree of T-cell activation induced. We demonstrate that high-level T-cell stimulation is likely to produce negative outcomes, both by failing to reduce viral reservoirs and by depleting the CD4 T-cell pool and disrupting CD4/CD8 T-cell homeostasis. In contrast, repeated low-level stimulation may both aid CD4 T-cell pool expansion and achieve a substantial reduction in the long-lived HIV-1 reservoir.

CONCLUSIONS

Our analysis suggests that although treatment that activates T-cells can reduce the long-lived HIV-1 reservoir, caution should be used as high-level stimulation may result in a negative outcome.

T-cell immunodeficiency following cytotoxic antineoplastic therapy: a review

Although cancer itself is immunosuppressive, cytotoxic antineoplastic therapy is the primary contributor to the clinical immunodeficiency observed in cancer patients. The immunodeficiency induced by cytotoxic antineoplastic therapy is primarily related to T-cell depletion, with CD4 depletion generally more severe than CD8 depletion. Myeloablative therapy, dose-intensive alkylating agents, purine nucleoside analogs, and corticosteroids substantially increase the risk of therapy-induced immunosuppression. Restoration of T-cell populations following cytotoxic antineoplastic therapy is a complex process. Efficient recovery of CD4+ T cell populations requires thymic-dependent pathways which undergo an age-dependent decline resulting in prolonged CD4+ T-cell depletion in adults following T-cell-depleting therapy. Total CD8+ T-cell numbers recover in both children and adults relatively quickly post-therapy; however, CD8+ subset disruptions often remain for a prolonged period. The clinical management of patients with therapy-induced T-cell depletion involves the maintenance of a high index of suspicion for opportunistic pathogens, irradiation of blood products, prophylaxis for viral infections, and reimmunization in selected clinical circumstances. Future research avenues include efforts to rapidly rebuild immunity following cytotoxic antineoplastic therapy so that immune-based therapies may be utilized immediately following cytotoxic therapy to target minimal residual neoplastic disease.