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

Long-lasting alterations of the immune system by ionizing radiation exposure: implications for disease development among atomic bomb survivors

PURPOSE

The immune systems of the atomic-bomb (A-bomb) survivors were damaged proportionately to irradiation levels at the time of the bombing over 60 years ago. Although the survivor's immune system repaired and regenerated as the hematopoietic system has recovered, significant residual injury persists, as manifested by abnormalities in lymphoid cell composition and function. This review summarizes the long-lasting alterations in immunological functions associated with atomic-bomb irradiation, and discusses the likelihood that damaging effects of radiation on the immune system may be involved partly in disease development so frequently observed in A-bomb survivors.

CONCLUSIONS

Significant immunological alterations noted include: (i) attrition of T-cell functions, as reductions in mitogen-dependent proliferation and interleukin-2 (IL-2) production; (ii) decrease in helper T-cell populations; and (iii) increase in blood inflammatory cytokine levels. These findings suggest that A-bomb radiation exposure perturbed one or more of the primary processes responsible for T-cell homeostasis and the balance between cell renewal and survival and cell death among naive and memory T cells. Such perturbed T-cell homeostasis may result in acceleration of immunological aging. Persistent inflammation, linked in some way to the perturbation of T-cell homeostasis, is key in addressing whether such noted immunological changes observed in A-bomb survivors are in fact associated with disease development.

Immune constitution monitoring after PBMC transplantation in complete DiGeorge syndrome: an eight-year follow-up

A young boy with a confirmed complete DiGeorge Syndrome (cDGS) underwent a peripheral blood mononuclear cell transplantation (PBMCT) from his HLA-identical sister at 4.5 years of age, without a conditioning regimen. Eight years later, he is healthy with good immunological functions in the presence of a stable mixed T-cell chimerism. Absence of recent thymic emigrants is confirmed. We observe an inverted CD4+/CD8+ ratio, related to the CD8 subset expansion, a skewing of the TCR repertoire, especially on the CD8+ subset and a telomere loss on the CD8+ cells compared to the donor. However, these anomalies do not seem to have an impact on functional immunity. PBMCT in cDGS using an HLA-matched sibling donor provides good long-lasting immunity and is an easy alternative to bone marrow transplantation and to thymic transplantation.

The lymph node in HIV pathogenesis

Since the earliest days of the AIDS epidemic, clinicians and researchers have recognized the importance of lymphoid tissue both in the clinical manifestations of disease and in its pathogenesis. Generalized lymphadenopathy was one of the earliest harbingers of AIDS in the United States and over the past 27 years an increasing body of evidence has implicated the lymphoid organs as central to the pathogenesis of immune deficiency in chronic HIV-1 infection. In this essay, we will review some of the data that have been accumulated and propose a testable model that may reconcile them.

Dynamics of T- and B-lymphocyte turnover in a natural host of simian immunodeficiency virus

Increased lymphocyte turnover is a hallmark of pathogenic lentiviral infection. To investigate perturbations in lymphocyte dynamics in natural hosts with nonpathogenic simian immunodeficiency virus (SIV) infection, the nucleoside analog bromodeoxyuridine (BrdU) was administered to six naturally SIV-infected and five SIV-negative sooty mangabeys. As a measure of lymphocyte turnover, we estimated the mean death rate by fitting a mathematical model to the fraction of BrdU-labeled cells during a 2-week labeling and a median 10-week delabeling period. Despite significantly lower total T- and B-lymphocyte counts in SIV-infected sooty mangabeys than in SIV-negative mangabeys, the turnover rate of B lymphocytes and CD4(+) and CD8(+) T lymphocytes was not increased in the SIV-infected animals. A small, rapidly proliferating CD45RA(+) memory subset and a large, slower-proliferating CD45RA(-) central memory subset of CD4(+) T lymphocytes identified in the peripheral blood of sooty mangabeys also did not show evidence of increased turnover in the context of SIV infection. Independently of SIV infection, the turnover of CD4(+) T lymphocytes in sooty mangabeys was significantly higher (P < 0.01) than that of CD8(+) T lymphocytes, a finding hitherto not reported in rhesus macaques or humans. The absence of aberrant T-lymphocyte turnover along with an inherently high rate of CD4(+) T-lymphocyte turnover may help to preserve the pool of central memory CD4(+) T lymphocytes in viremic SIV-infected sooty mangabeys and protect against progression to AIDS.

T cell immune reconstitution following lymphodepletion

T cell reconstitution following lymphopenia from chemotherapy or stem cell transplant is often slow and incompetent, contributing to the development of infectious diseases, relapse, and graft-versus-host disease. This is due to the fact that de novo T cell production is impaired following cytoreductive regimens. T cells can be generated from two pathways: (1) thymus derived through active thymopoiesis and (2) peripherally expanded clones through homeostatic proliferation. During recovery from lymphopenia, the thymic pathway is commonly compromised in adults and T cells rely upon peripheral expansion to restore T cell numbers. This homeostatic proliferation exploits the high cytokine levels following lymphopenia to rapidly generate T cells in the periphery. Moreover, this early peripheral expansion of T cells can also be driven by exogenous antigen. This results in loss of T cell repertoire diversity and may predispose to auto- or allo-immunity. Alternatively, the high homeostatic proliferation following lymphopenia may facilitate expansion of anti-tumor immunity. Murine and human studies have provided insight into the cytokine and cellular regulators of these two pathways of T cell generation and the disparate portraits of T cell immunity created through robust thymopoiesis or peripheral expansion following lymphopenia. This insight has permitted the manipulation of the immune system to maximize anti-tumor immunity through lymphopenia and led to an appreciation of mechanisms that underlie graft versus host disease.

Generation of pro-T cells in vitro: potential for immune reconstitution

Immunodeficient individuals are susceptible to opportunistic infection. While stem cell transplantation can restore a functional immune system, T cells are slow to recover and limited in eliciting adaptive immune responses. Approaches to selectively enhance T cell function have focused on boosting thymopoiesis to generate new T cells or expanding existing T cells. By taking advantage of the role of Notch signaling in T cell development, we have developed an in vitro system able to generate large numbers of progenitor T cells from human hematopoietic stem cells. Here, we discuss this in vitro system and its implications for the potential treatment of T cell immunodeficiency.

Antigen-Specific T-Cell Immunity in Multiple Myeloma Patients is Restored Following High-Dose Therapy: Implications for Timing of Vaccination

The present study analyses the influence of high-dose chemotherapy (HD) and autologous stem cell transplantation on natural and vaccine induced specific immunity in multiple myeloma patients. Peripheral blood was collected from six multiple myeloma (MM) patients at serial time points in connection with treatment and during a follow-up period of 3 months. T-cell response to cytomegalovirus (CMV), varicella zoster virus (VZV) and tetanus toxoid (TT) was determined by flow cytometry analysis for CD69, TNFalpha, IFNgamma, IL-4 expression and cell proliferation. At diagnosis and prior to induction chemotherapy TNFalpha expressing T cells in 5/6 patients were found specific for CMV, 3/6 for VZV and 4/6 for TT. Serial analyses during treatment conclude impaired immune response, however, 3 months post-transplantation all but one patient had regained cytokine expressing CD8(+) T cells specific for CMV, VZV and TT. The highest percentages of cytokine responding T cells were observed after stimulation with CMV antigen. A striking observation was the low cytokine reactivity (close to zero) measured in G-CSF mobilized blood at the time of leukapheresis. In spite of a general reduction of the CD4/CD8 ratio following transplantation, recovery of antigen specific CD4(+) T cells reactivity generally occurred prior to CD8(+) recovery and often to a higher level. In conclusion, the study demonstrates that natural as well as vaccine induced specific immunity present prior to HD was regained after stem cell transplantation, hence identifying a possible window for future vaccination trials.

Immunobiology of allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) has evolved into an effective adoptive cellular immunotherapy for the treatment of a number of cancers. The immunobiology of allogeneic HSCT is unique in transplantation in that it involves potential immune recognition and attack between both donor and host. Much of the immunobiology of allogeneic HSCT has been gleaned from preclinical models and correlation with clinical observations. We review our current understanding of some of the issues that affect the success of this therapy, including host-versus-graft (HVG) reactions, graft-versus-host disease (GVHD), graft-versus-tumor (GVT) activity, and restoration of functional immunity to prevent transplant-related opportunistic infections. We also review new strategies to optimize the GVT and improve overall immune function while reducing GVHD and graft rejection.

T cells remaining after intensive chemotherapy for acute myelogenous leukemia show a broad cytokine release profile including high levels of interferon-gamma that can be further increased by a novel protein kinase C agonist PEP005

Cytokines are released during T cell activation, including the potentially anti-leukemic interferon-gamma (IFNgamma), but also the hematopoietic growth factor granulocyte-macrophage colony-stimulating factor (GM-CSF) that enhance proliferation and inhibit apoptosis of acute myelogenous leukemia (AML) cells. In the present study we investigated the release of IFNgamma and GM-CSF by circulating T cells in AML patients with chemotherapy-induced cytopenia. T cells were activated with anti-CD3 plus anti-CD28 in a whole-blood assay in the presence of their natural cytokine network. We examined 63 samples derived from 16 AML patients during 28 chemotherapy cycles. Activated T cells showed a broad cytokine release profile, but IFNgamma and GM-CSF levels showed a significant correlation and were generally higher than the other cytokine levels. Higher IFNgamma and GM-CSF responses were associated with a low CD4:CD8 ratio, older patient age and no ongoing chemotherapy indicating potential utility of T cell activation regimes for the older AML patient. The cytokine levels could be further increased by the novel protein kinase C agonist PEP005, which also induced significant production of IL2 and TNFalpha which could contribute to anti-tumor effects in AML patients. We conclude that remaining T cells after intensive AML therapy show a broad cytokine release profile including high and significantly correlated levels of potentially anti-leukemic IFNgamma and the AML growth factor GM-CSF. The final outcome of an AML-initiated T cell cytokine response will thus depend on the functional characteristics of the AML cells, in particular the relative expression of IFNgamma and GM-CSF receptors which differs between AML patients.

High-dose cyclophosphamide inhibition of humoral immune response to murine monoclonal antibody 3F8 in neuroblastoma patients: broad implications for immunotherapy

BACKGROUND

The murine monoclonal antibody 3F8 mediates lysis of neuroblastoma (NB) by complement and leukocytes (including neutrophils) but is neutralized if human anti-mouse antibody (HAMA) forms. We assessed the impact on rapid HAMA formation of prior chemotherapy in NB patients.

METHODS

For the 153 patients treated with 3F8 after conventional therapy (Group 1), the analysis included time from chemotherapy to the start of 3F8. For the 103 patients treated with 3F8 after myeloablative alkylator-based therapy (MAT) (Group 2), the analysis included both chemotherapy administered before stem-cell collection and time from MAT to the start of 3F8.

RESULTS

In Group 1, the incidence of HAMA-positivity was significantly lower if patients received high-dose cyclophosphamide (HD-Cy, > or = 4,000 mg/m2) before 3F8 treatment (P < 0.001). In addition, HAMA-positivity was least likely if 3F8 treatment was initiated <90 days post-HD-Cy (2/76 compared to 3/19 first treated at 90-120 days, and 17/27 first treated at >120 days, P < 0.001). In Group 2 patients who were transplanted with stem cells collected after HD-Cy, HAMA-positivity occurred in 1/60 patients treated <90 days post-MAT versus 13/23 treated >90 days post-MAT (P < 0.001). Among Group 2 patients transplanted with stem cells collected after no prior HD-Cy, the incidence of HAMA-positivity was significantly higher (15/19, P < 0.001), including 5/7 whose 3F8 treatment began <90 days post-MAT.

CONCLUSIONS

HD-Cy reliably blocks humoral responses to a murine antibody. This capacity to prevent host rejection of foreign or not fully humanized proteins raises the possibility of a broad role for HD-Cy in immunotherapeutic strategies.

Long-Term Cell Monitoring of Kidney Recipients After an Antilymphocyte Globulin Induction With and Without Steroids

BACKGROUND

Because of several side effects, the corticosteroid usage has been minimized in kidney transplantation. The increased acute rejection episodes associated with their withdrawal may counterbalance with induction treatment using polyclonal antilymphocyte globulin (ALG). The effects of ALG on blood cell phenotype have already been the subject of several reports. However, to date, no data are available concerning the comparison of blood phenotype when ALG is given with or without steroids and no gene profiling study has been performed.

METHODS

We report here on a longitudinal blood cell analysis of a selected cohort of kidney recipients enrolled in a randomized study of steroid avoidance or withdrawal (during 6 months) during ALG induction.

RESULTS

In the two groups, ALG quickly and massively depleted all the T cells and natural killer cells, but not B cells. Interestingly, the lymphopenia-driven homeostatic proliferation of CD4 and CD8T cells strongly differed with persistent low CD4 (including CD25CD4) T-cell counts. Effector memory CD8T cells reappeared rapidly. ALG induced apoptosis-associated molecules and increased myeloid cell genes. However, few genes were found differentially expressed with a low fold ratio between the two groups during and at distance of corticotherapy.

CONCLUSION

Thus initial steroid avoidance or withdrawal associated with ALG induction has a weak influence on phenotype and transcriptional pattern of blood leukocytes. In contrast, ALG therapy induces an early and strong depletion of all T-cell subsets with contrasted long-lasting homeostatic regulation.

Vaccination regimens incorporating CpG-containing oligodeoxynucleotides and IL-2 generate antigen-specific antitumor immunity from T-cell populations undergoing homeostatic peripheral expansion after BMT

Development of CD8(+) T-cell responses targeting tumor-associated antigens after autologous stem cell transplantations (ASCTs) might eradicate residual tumor cells and decrease relapse rates. Because thymic function dramatically decreases with aging, T-cell reconstitution in the first year after ASCT in middle-aged patients occurs primarily by homeostatic peripheral expansion (HPE) of mature T cells. To study antigen-specific T-cell responses during HPE, we performed syngeneic bone marrow transplantations (BMTs) on thymectomized mice and then vaccinated the mice with peptides plus CpG-containing oligodeoxynucleotides (CpGs) in incomplete Freund adjuvant and treated the mice with systemic interleukin-2 (IL-2). When CD8(+) T-cell responses were measured ex vivo, up to 9.1% of CD8(+) T cells were specific for tumor-associated epitopes. These large T-cell responses were generated by synergism between CpG and IL-2. When we injected mice subcutaneously with tumor cells 14 days after BMT and then treated them with peptide + CpG-containing vaccines plus systemic IL-2, survival was increased and tumor growth was inhibited in an epitope-specific manner. Depletion of CD8(+) T cells eliminated epitope-specific antitumor immunity. This is the first report to demonstrate that CD8(+) T-cell responses capable of executing antitumor immunity can be elicited by CpG-containing vaccines during HPE.

Homeostatic expansion and repertoire regeneration of donor T cells during graft versus host disease is constrained by the host environment

Graft versus host disease (GVHD) typically results in impaired T-cell reconstitution characterized by lymphopenia and repertoire skewing. One of the major causes of inadequate T-cell reconstitution is that T-cell survival and expansion in the periphery are impaired. In this report, we have performed adoptive transfer studies to determine whether the quantitative reduction in T-cell numbers is due to an intrinsic T-cell defect or whether the environmental milieu deleteriously affects T-cell expansion. These studies demonstrate that T cells obtained from animals with graft-versus-host disease (GVHD) are capable of significant expansion and renormalization of an inverted CD4/CD8 ratio when they are removed from this environment. Moreover, these cells can generate complex T-cell repertoires early after transplantation and are functionally competent to respond to third-party alloantigens. Our data indicate that T cells from mice undergoing GVHD can respond to homeostatic signals in the periphery and are not intrinsically compromised once they are removed from the GVHD environment. We thereby conclude that the host environment and not an intrinsic T-cell defect is primarily responsible for the lack of effective T-cell expansion and diversification of complex T-cell repertoires that occurs during GVHD.

Combination of Transient Lymphodepletion With Busulfan and Fludarabine and Peptide Vaccination in a Phase I Clinical Trial for Patients With Advanced Melanoma

Taking advantage of homeostatic mechanisms to boost tumor-specific cellular immunity is raising increasing interest in the development of therapeutic strategies in the treatment of melanoma. Here, we have explored the potential of combining homeostatic proliferation, after transient immunosuppression, and antigenic stimulation of Melan-A/Mart-1 specific CD8 T-cells. In an effort to develop protocols that could be readily applicable to the clinic, we have designed a phase I clinical trial, involving lymphodepleting chemotherapy with Busulfan and Fludarabine, reinfusion of Melan-A specific CD8 T-cell containing peripheral blood mononuclear cells (exempt of growth factors), and Melan-A peptide vaccination. Six patients with advanced melanoma were enrolled in this outpatient regimen that demonstrated good feasibility combined with low toxicity. Consistent depletion of lymphocytes with persistent increased CD4/CD8 ratios was induced, although the proportion of circulating CD4 regulatory T-cells remained mostly unchanged. The study of the immune reconstitution period showed a steady recovery of whole T-cell numbers overtime. However, expansion of Melan-A specific CD8 T-cells, as measured in peripheral blood, was mostly inconsistent, accompanied with marginal phenotypic changes, despite vaccination with Melan-A/Mart-1 peptide. On the clinical level, 1 patient presented a partial but objective antitumor response following the beginning of the protocol, even though a direct effect of Busulfan/Fludarabine cannot be completely ruled out. Overall, these data provide further ground for the development of immunotherapeutic approaches to be both effective against melanoma and applicable in clinic.

Interleukin-7 Immunotherapy

IL-7 is a member of the common gamma-chain family of cytokines sharing a common gamma-chain in their receptor. Beyond its long-established pivotal role in immune development, it has been more recently recognized as a critically important regulator of peripheral naïve and memory T cell homeostasis while its role in postdevelopment thymic function remains at best, poorly defined, and controversial. Its multiple immune-enhancing properties, most notably in the maintenance of T cell homeostasis, make it a very attractive candidate for immunotherapy in a wide variety of clinical situations. Following many years of rich preclinical data in murine and simian models, IL-7 is now emerging in human phase I trials as a very promising immunotherapeutic agent. Human in vivo data discussed here are derived from the phase I study initiated at the National Cancer Institute in collaboration with Cytheris, Inc., in a cohort of subjects with incurable malignancy.

Distinct patterns of regeneration of central memory, effector memory and effector TCD8+ cell subsets after different hematopoietic cell transplant types: Possible influence in the recovery of anti-cytomegalovirus immune response and risk for its reactivation

TCD8+ cells may be divided into subsets with different phenotypes and functions: naive, central memory, effector memory and effector. Aiming to better understand the differences in early reconstitution of these TCD8+ cell subsets and their relationship with post-transplant anti-cytomegalovirus (CMV) immune responses recovery, we prospectively analyzed the transfer and expansion of these subsets in different transplant types. We found that graft cells from donor's peripheral blood, either allogeneic or autologous, were enriched for central memory, effector memory and effector phenotypes compared to allogeneic bone marrow grafts, as assessed by surface markers phenotyping and granzyme B expression. However, post-transplant, these subsets expanded in autologous recipients only, reaching numbers much greater than in allo-recipients at days +29 and +96. At the same time, autologous recipients presented less CMV reactivation and more vigorous CMV-induced interferon-gamma and lymphoproliferative responses. The marked loss of allo-transferred memory TCD8+ cells was probably due to the fact that they were more activated and more prone to apoptosis than auto-transferred TCD8+ cells as assessed by CD69 and active caspase 3 expression. Thus, transfer of peripheral blood stem cells in the allogeneic but not autologous setting is associated with poor expansion of memory TCD8+ cells, probably delaying antiviral immune reconstitution. These data may have important implications for the design of better strategies to immunoprotect this population against infectious challenges since different transplant types have different potentials for memory TCD8+ cells transfer and expansion.

T-lymphocyte reconstitution following rigorously T-cell-depleted versus unmodified autologous stem cell transplants

We compared the kinetics of T-cell recovery after extensive ex vivo and in vivo T-cell depleted autologous stem cell transplantation (SCT) for multiple sclerosis (MS; n=8) with unmodified SCT for hematological malignancies (HM; n=39). Both patient group showed a very protracted recovery of 'naive' CD4(+), 45R0(-) ( approximately CD45RA(+)) T-cells. Within the 'primed' CD4(+), 45R0(+) T-cells, the 'central memory' cells expressing the CD62L and CD27 markers were the slowest to recover. The repopulating T-cells were highly activated, as shown by increased expression of HLA-DR and the apoptosis marker CD95. The capability of CD4(+) and CD8(+) T-cells to produce IFN-gamma, IL-2 and TNF-alpha had reached normal ranges from 2 months post SCT onwards. Unexpectedly, the kinetics of T-cell recovery between 3 and 12 months post transplant was similar in T-depleted and unmodified SCT. Before SCT, the HM patients showed lymphopenia of all T-cell subsets, upregulated HLA-DR and CD95 expression and increased cytokine responses. We suggest that the similar kinetics of T-cell recovery in the two patient groups may be explained by the susceptibility to apoptosis of the activated CD4(+) T-cells in the autografts of the HM patients. This susceptibility to apoptosis would interfere with a swift and sustained CD4(+) T-cell regeneration post SCT.

Immune reconstitution and predictors of virologic failure in adolescents infected through risk behaviors and initiating HAART: week 60 results from the PACTG 381 cohort

The responses to HAART in HIV-infected adolescents infected through risk behaviors are not well defined. PACTG 381 collected intensive immunologic and virologic data on youth naive to or with minimal exposure to antiretroviral therapy who began HAART. Subjects were evaluated according to their weeks 16-24 virologic response. Comparisons with a cohort of HIV-uninfected adolescents from the REACH cohort were performed. Cox proportional hazards models were used to identify baseline and week 24 predictors of virologic failure. Only 69 of 120 subjects (58%) achieved virologic suppression by weeks 16-24, whereas 55 of 69 (80%) demonstrated control to week 60. Higher CD4+ naive T cells (CD4+/62L+/RA+: hazard ratio [HR], 2.13; p = 0.018), higher CD8+ activated T cells (CD8+/CD38+/DR+: HR, 1.40, p = 0.028 per 100 cells/mm3) and higher CD8+ naive T cells (CD8+/62L+/RA+: HR, 1.72; p = 0.005) at weeks 16-24 in subjects with early viral success were predictive of subsequent failure. By week 60, total CD4+ T cells remained significantly lower than in uninfected controls. Adolescents beginning HAART achieve moderate rates of viral suppression by weeks 16-24. In those who do achieve early virologic control, suppression to week 60 is high although total CD4+ T cells remain significantly lower than in uninfected controls. Several T cell markers were predictive of subsequent virologic failure in subjects achieving short-term success. Further study is warranted to determine whether these predictors provide any benefit to clinical management.

Thymic Hyperplasia after Adjuvant Chemotherapy in Breast Cancer

We report 2 patients with breast cancer who were treated with surgery and adjuvant chemotherapy for stage IIa and stage I breast cancers. Follow-up CT scans showed an anterior mediastinal mass, raising concern for tumor recurrence. Thymectomy performed on the first patient, and close follow-up with radiographic studies on the second patient, revealed benign thymic enlargement. Thymic hyperplasia can occur after cytotoxic chemotherapy and may be due to rebound enlargement after initial atrophy caused by chemotherapy. Thymic hyperplasia after chemotherapy has been reported mostly in young age groups and is described in the literature to be associated with various types of cancers, including lymphomas, leukemias, testicular cancer, and sarcomas, and in the stem cell transplant setting. This is the first case series describing 2 patients with early stage breast cancer who, following adjuvant standard dose chemotherapy, developed thymic hyperplasia. Awareness of this unusual side effect in patients treated with chemotherapy may prevent unnecessary investigation and surgical intervention.

Renewing the T cell repertoire to arrest autoimmune aggression

There is now evidence that high-dose immune ablation and autologous hematopoietic stem cell transplantation in humans triggers a reconstitution program that leads to the comprehensive renewal of the T cell repertoire. We argue here that several features of this program help to explain how autologous hematopoietic stem cell transplantation can induce long-term clinical remission from organ-specific-, as well as systemic, autoimmune diseases. We propose a model envisioning a coordinated sequence of events, rebuilding an immune system that is competent against infection but that is substantially reconfigured in a way that is less likely to redevelop autoimmunity.

Reconstitution of adaptive and innate immunity following allogeneic hematopoietic stem cell transplantation in humans

Allogeneic hematopoietic stem cell transplantation is a potentially curative treatment modality for a number of hematologic malignancies, as well as inherited immunodeficiencies and hemoglobinopathies, and may also have a role in selected acquired autoimmune disorders. The complete or near-complete ablation of host immunity and subsequent establishment of donor-derived immunity that is required for successful engraftment and long-term outcomes provide a major obstacle to such transplantation approaches. A delicate balance exists between the need for the reconstituted donor-derived immunity to provide both protection against pathogenic challenges and graft-versus-malignancy activity, and the potentially harmful expansion of alloreactive T-cell clones mediating GvHD. The search for interventions that would allow more rapid and selective reconstitution of beneficial immune specificities continues to be informed by the development of new tools enabling a more precise dissection of the kinetics of reconstituting populations. This review summarizes more recent data on immune reconstitution following allogeneic transplantation in humans.

Immunity for tumors and microbes after autotransplantation: if you build it, they will (not) come

Relapses after autologous stem cell transplants for hematopoietic malignancies are frequent and post-transplant infections continue to cause significant post-transplant morbidity and even mortality. The post-transplant period is typically characterized by low lymphocyte counts and impaired immune cell function. Early restoration of immune function may contribute to better disease control and enhance protection from infections. Indeed the attainment of a 'minimal residual disease' status following high-dose therapy makes the early post-transplant period ideal for the introduction of antitumor immunotherapy. Attempts to generate immunity against tumor and microbial antigens after autotransplantation have included vaccinations, T cell infusions (both resting and activated) and combinations of vaccinations and adoptive T cell infusions. One successful strategy for generating robust immune responses against microbial antigens was the combination of pre and post-transplant immunizations along with an early (post-transplant) infusion of in vivo vaccine-primed and ex vivo co-stimulated autologous T cells. Whether this or similar strategies will lead to the generation of effective antitumor immunity is unknown. The lessons gained from efforts to rebuild immune system function in the setting of autotransplantation may also be applicable to the problem of restoring immunity in other immunodeficient groups such as patients with cancer or HIV disease and the elderly.

Cell-mediated immune responses to influenza vaccination in healthy volunteers and allogeneic stem cell transplant recipients

Influenza is one of the most common respiratory diseases in humans. The response to vaccination is frequently poor in immunosuppressed individuals. The aim of the present study was to develop an enzyme-linked immunospot (ELISPOT) assay for measuring of the specific T-cell response to influenza vaccination. In all, 18 healthy subjects and six stem cell transplantation (SCT) patients tested before and 4 weeks after influenza vaccination were included in the present study. Peripheral blood lymphocytes were stimulated with four influenza peptides; three based on sequences from the hemagglutinin and one from the M1 protein. The ELISPOT assay and the measurement of intracellular IFN-gamma production were used to determine the cell-mediated responses after stimulation with the peptides. Influenza vaccination elicited strong cell-mediated immune responses in the healthy controls to all four peptides with 3.2-6.9-fold increases in the number of IFN-gamma producing spots/10(6) cells. By intracellular staining, it was suggested that CD4+ cells mediated the responses to the hemagglutinin peptides. In contrast, there was no increase in the number of IFN-gamma producing cells response after vaccination in the six SCT patients. In conclusion, our results suggest that the ELISPOT assay might be used as a complement to serology for monitoring of future influenza vaccine studies in SCT patients.

CD11chighDendritic Cell Ablation Impairs Lymphopenia-Driven Proliferation of Naive and Memory CD8+T Cells

The peripheral lymphocyte pool size is governed by homeostatic mechanisms. Thus, grafted T cells expand and replenish T cell compartments in lymphopenic hosts. Lymphopenia-driven proliferation of naive CD8+ T cells depends on self-peptide/MHC class I complexes and the cytokine IL-7. Lymphopenia-driven proliferation and maintenance of memory CD8+ T cells are MHC independent, but are believed to require IL-7 and contact with a bone marrow-derived cell that presents the cytokine IL-15 by virtue of its high affinity receptor (IL-15Ralpha). In this study we show that optimal spontaneous proliferation of grafted naive and memory CD8+ T cells in mice rendered lymphopenic through gene ablation or irradiation requires the presence of CD11chigh dendritic cells. Our results suggest a dual role of CD11chigh dendritic cells as unique APC and cytokine-presenting cells.

Role of bcl-2 mRNA in homeostatic proliferation in circulating T-cells in human liver transplant patients after T-cell depletion

BACKGROUND

Prolonged T-cell depletion after liver transplantation leads to life-threatening infections. Members of the anti-apoptotic Bcl-2 gene family can maintain T-cell viability. T-cell numbers and their Bcl-2 expression following living donor liver transplantation (LDLT) were analyzed in 108 surviving and 13 deceased recipients.

MATERIALS AND METHODS

Bcl-2 mRNA levels and phenotypic changes of T-cells were examined by quantitative PCR and by measuring expression of CD45RO and CCR7.

RESULTS

Based on the restoration of peripheral T-cell numbers, the 108 surviving recipients were classified into three groups. All recipients showed T-cell depletion, down to approximately 30% of pretransplant levels within 3 h of graft reperfusion. In Group I, the T-cell numbers were rapidly restored to pretransplant levels, within 5 days, with a rapid decrease in Bcl-2 mRNA levels immediately after LDLT. In Group II, the T-cell numbers were restored to normal levels by 19 days, with down-regulation of Bcl-2 mRNA. In Group III, the T-cell numbers were maintained at low levels for much longer, with high levels of Bcl-2 mRNA. In all three groups of recipients, there was statistically significant (r = -0.78) inverse correlation between T-cell numbers and Bcl-2 mRNA.

CONCLUSIONS

For successful transplantation, homeostatic restoration of T-cells must occur as soon as possible. Evaluation of peripheral T-cell numbers and of Bcl-2 expression may have therapeutic potential in identifying those transplant patients who face increased risk of infection.

Establishing a platform for immunotherapy: clinical outcome and study of immune reconstitution after high-dose chemotherapy with progenitor cell support in breast cancer patients

Tumor vaccine after high-dose chemotherapy (HDC) and autologous stem cell transplantation (ASCT) aims at directing immune recovery toward tumor responses after optimizing minimal residual disease. We have characterized T-cell recovery and tumor response after a regimen devised as a platform for such immunotherapy. One hundred patients with high-risk or metastatic breast cancer received 3 to 7 cycles of paclitaxel and cyclophosphamide (overall response rate, 78%) and then HDC with melphalan and etoposide. Seventy-one patients received HDC and ASCT (no mortality at 100 days). At 24 months after transplantation, progression-free and overall survival probabilities for patients with stage IIIA, IIIB, and IV disease were 82%, 81%, and 42% and 100%, 94%, and 68%, respectively. The median progression-free and overall survivals from entry on study for stage IV patients were 15.3 and 38.1 months, respectively. CD3 + , CD8 + , and CD4 + cells were severely depleted after ASCT. Although total CD8 + T-cell numbers approached the normal range by 3 months, most of these cells were CD28 - . Naive CD45RA + CD4 + T cells approached the normal range only 18 months after ASCT and only in younger patients. The described observations provide the basis for devising a strategy for cancer vaccine administration after ASCT. Incorporating immune reconstitution enhancement after ASCT may be advantageous.

Effects of Castration on Thymocyte Development in Two Different Models of Thymic Involution

Age-associated thymic involution is accompanied by decreased thymic output. This adversely affects general immune competence and T cell recovery following cytoreductive treatments such as chemotherapy. A causal link between increasing sex steroids and age-related thymic atrophy is well established. Although castration has been demonstrated to regenerate the atrophied thymus, little is known about how this is initiated or the kinetics of thymocyte regeneration. The present study shows that although castration impacts globally across thymocyte development in middle-aged mice, the regenerative effects are initiated in the immature triple-negative compartment and early T lineage progenitors (ETP). Specifically, there was a reduction in number of ETP with age, which was restored following castration. There was, however, no change in ETP reconstitution potential in ETP at this age or following castration. Furthermore, in a chemotherapy-induced model of thymic involution, we demonstrate castration enhances intrathymic proliferation and promotes differentiation through the triple-negative program. Clinically, reversible sex steroid ablation is achieved hormonally, and thus presents a means of ameliorating immune inadequacies, for example, following chemotherapy for bone marrow transplantation. By improving our understanding of the kinetics of thymic recovery, this study will allow more appropriate timing of therapy to achieve maximal reconstitution, especially in the elderly.

T-cell reconstitution and expansion after hematopoietic stem cell transplantation: 'T' it up!

Adoptive immunotherapy is the isolation and infusion of antigen-specific or nonspecific lymphocytes. Adoptive therapy with T cells may have a role in replacing, repairing, or enhancing immune function damaged by cytotoxic therapies, and rapid lymphocyte recovery may improve outcome after autologous and allogeneic stem cell transplantation (SCT). Recently, a plethora of information on the basic mechanisms of T-cell biology and regulation of cellular immune responses has emerged, permitting the development of new forms of adoptive cell therapy. Efficient ex vivo culture method for T-cell subsets affords the possibility of adoptive transfer of T cells engineered with enhanced capacity for central memory, effector cytotoxicity, Th1, Th2, veto cell, and T regulatory functions. Studies show that homeostatic T-cell proliferation is important for effective adoptive immunotherapy and pretreatment with chemotherapy may enhance the effects of infused T cells. Replicative senescence, in part due to telomere erosion, likely limits successful adoptive immunotherapy, though it may be possible to maintain T-cell pools by enforced expression of telomerase. Clinical trials now demonstrate that it is possible to enhance immune reconstitution after SCT with cytokines or infusions of ex vivo costimulated expanded T cells. These data all support the premise that adoptive therapy can accelerate reconstitution of cellular immunity with enhanced antitumor effects following SCT.

Age-related thymic activity in adults following chemotherapy-induced lymphopenia

BACKGROUND

The potential role of the adult thymus in T-cell homeostasis subsequent to lymphopenia remains the subject of debate. We examined whether thymic activity contributes to reconstitution of the peripheral T-cell pool, a critical process for patients recovering from antineoplastic therapy.

METHODS

In selected patients with various neoplastic diseases we assessed peripheral blood lymphocyte subsets by flow-cytometry, including thymus-derived, CD4+ T cells expressing the CD45RA molecule, and thymic size rebound by CT scan before, and 3, 6 and 12 months after completion of cytotoxic therapy.

RESULTS

Adult patients (n = 21, mean age of 30 years, range 18-49) had higher baseline numbers of B and lower numbers of NK cells than elderly patients (n = 15, mean age of 79 years, range 70-91), while total T-cell numbers did not differ. Despite the reduction of lymphocyte counts being comparable in the adult (mean of 45%) and elderly (mean of 49%) groups, occurring at, or near, completion of treatment, an enlargement of the previously atrophic thymus was evident in 63% of the adult, but in none of the elderly, subjects. In 22 patients who remained active disease-free during the following year, B cells and NK cells recovered to pretreatment levels as soon as at 3 months, whereas overall T-cell recovery occurred at 6 months post-treatment. Thymic rebound, observed in 11 of 22 patients who were of younger age, correlated significantly with a faster and more complete recovery of CD45RA+ CD4+ (mainly helper-naïve) T cells.

CONCLUSION

The adult thymus appears capable of regeneration, at least up to middle age, contributing significantly to the reconstitution of the peripheral T-cell pool following chemotherapy-induced lymphopenia. In advanced age, however, although peripheral homeostatic pathways appear intact, regeneration of the naïve repertoire is incomplete.

Antigen-specific T-cell memory is preserved in children treated for acute lymphoblastic leukemia

Despite profound T-cell immunodeficiency, most patients treated with chemotherapy do not succumb to infection. The basis for residual protective immunity in lymphopenic patients is not known. We prospectively measured T-cell numbers, thymopoiesis, and T-cell memory in 73 children undergoing a 2-year chemotherapy regimen for acute lymphoblastic leukemia (ALL) and compared them to an age-matched cohort of 805 healthy children. Most patients had profound defects in CD4 and CD8 T-cell numbers at diagnosis that did not recover during the 2 years of therapy. Thymic output and the fraction of naive T cells were significantly lower than in healthy controls. However, the remaining T-cell compartment was enriched for antigen-experienced, memory T cells defined both by phenotype and by function. This relative sparing of T-cell memory may, in part, account for the maintenance of protective immunity in lymphopenic patients treated for ALL. Moreover, because the memory T-cell compartment is least affected by ALL and its treatment, strategies to induce immunity to pathogens or tumor antigens in cancer patients may be most successful if they seek to expand pre-existing memory T cells.

Immune reconstitution after childhood acute lymphoblastic leukemia is most severely affected in the high risk group

OBJECTIVE

The aim was to examine the immune reconstitution after current chemotherapy for childhood ALL, with a special focus on finding immunologic variables that predict a poor immune response to vaccinations.

PROCEDURE

In a cross-sectional study of 31 children after treatment with the NOPHO ALL-1992 protocol peripheral blood lymphocyte subsets, T- and B-cell function in vitro and serum immunoglobulins (Ig) were measured. All patients were examined once, at 1 or at 6 months after cessation of chemotherapy, immediately before vaccination with DT and Hib.

RESULTS

Lymphocytes, T-cells, and CD4+ T-cells were low at 6 months after treatment. Naive T-cell subsets were more reduced than memory subsets. In the high risk (HR) ALL group, CD8+ T-cells were reduced at 6 months. NK-cells were low at 1 month, but normal at 6 months; however, the CD3+CD56+ (NKT) subset was reduced at both time points. Total B-cell number was low at 1 month, but normal at 6 months. A relative increase of CD5+ B-cells (B-1 cells) was evident, particularly in the HR group. Antigen-independent T- and B-cell function in vitro were affected at 1 month, but virtually normalized at 6 months. Serum IgM level was decreased at 1 month and IgG3 level was increased at 1 and 6 months.

CONCLUSIONS

This study shows that immune reconstitution after childhood ALL is slower than previously reported and emphasizes the influence of treatment intensity. The most intensively treated patients still have persistent abnormalities in T-, B-, and NK-cell subsets at 6 months post therapy and show a poor response to immunization with T-cell dependent antigens. In the HR group, routine re-immunizations before this time point are of limited benefit, and the effect of repeated vaccinations should be evaluated.

Results of a Phase I study utilizing monocyte-derived dendritic cells pulsed with tumor RNA in children with Stage 4 neuroblastoma

BACKGROUND

A Phase I study of 11 pediatric patients with newly diagnosed, Stage 4 neuroblastoma was conducted using monocyte-derived dendritic cells (DC) pulsed with tumor RNA to produce antitumor vaccines (DC(RNA)).

METHODS

Patients received two courses of induction with carboplatin followed by standard chemotherapy, surgery, radiation, high-dose therapy, stem cell rescue, and DC(RNA) vaccine therapy.

RESULTS

The results showed that this method for producing and administering DC(RNA) from a single leukapheresis product was both feasible and safe in this pediatric neuroblastoma population. Two courses of carboplatin maintained lymphocyte counts at normal levels. However, immune function 6 weeks after high-dose chemotherapy and stem cell rescue and prior to receiving DC(RNA) was impaired in all patients tested. There was an alteration in the ratio of CD4-positive and CD80-positive T cells. CD4-positive cell numbers were below normal, whereas CD8-positive cell numbers were above normal for all patients. In addition, CD19-positive cell numbers were below normal for all but one patient. It was found that humoral responses to recall antigens (diphtheria and tetanus) and cellular responses to mitogen and recall antigens were below normal in most patients. Despite this, two of three patients tested showed a tumor-specific humoral immune response to DC(RNA). Among the patients who had measurable disease at the time of DC(RNA) vaccine, none showed any objective tumor response.

CONCLUSIONS

DC(RNA) vaccines were both safe and feasible in children with Stage 4 neuroblastoma. Humoral responses to tumor were detected, although remained immunosuppressed at the time of administration, limiting efficacy.

Partial immune reconstitution following highly active antiretroviral therapy: can adjuvant interleukin-2 fill the gap?

Highly active antiretroviral therapy (HAART) induces a substantial control of HIV viral replication, but it allows for only a partial immune reconstitution, thus prompting the rationale for the adjuvant use of immunomodulants. Based on its in vitro action as a major T cell growth factor, interleukin (IL)-2 has now been extensively investigated for its potential to correct the HIV-driven immune deficiencies, possibly translating into immunological control over HIV infection. Specific immunological end points have thus far been addressed within extensive Phase I/II trials, disclosing a broad insight into several aspects of the IL-2-mediated immune reconstitution allowing for interesting clinical speculation. Indeed, preliminary results indicate that adjuvant IL-2 induces a significant CD4 cell rescue in patients with no immune recovery following long-term HAART, thus standing as a valid and safe therapeutic option for these patients. Furthermore, in these patients, the IL-2-mediated immune reconstitution is characterized by a rise in both peripheral turnover and de novo T cell synthesis, with reversion of the skewed HIV-driven immunophenotypic pattern, a substantial increase in IL-7 production and in several markers of immune function. Combined, these findings indicate IL-2 has a beneficial effect in correcting the severe disruption in T cell homeostasis induced by HIV, through the interaction with T cells and cytokine microenvironment. However, whether or not these immunological effects translate into an actual immunological competency and therefore clinical benefit, still awaits demonstration from ongoing large, controlled clinical studies.

Thymic output generates a new and diverse TCR repertoire after autologous stem cell transplantation in multiple sclerosis patients

Clinical trials have indicated that autologous hematopoietic stem cell transplantation (HSCT) can persistently suppress inflammatory disease activity in a subset of patients with severe multiple sclerosis (MS), but the mechanism has remained unclear. To understand whether the beneficial effects on the course of disease are mediated by lympho-depletive effects alone or are sustained by a regeneration of the immune repertoire, we examined the long-term immune reconstitution in patients with MS who received HSCT. After numeric recovery of leukocytes, at 2-yr follow-up there was on average a doubling of the frequency of naive CD4⁺ T cells at the expense of memory T cells. Phenotypic and T cell receptor excision circle (TREC) analysis confirmed a recent thymic origin of the expanded naive T cell subset. Analysis of the T cell receptor repertoire showed the reconstitution of an overall broader clonal diversity and an extensive renewal of clonal specificities compared with pretherapy. These data are the first to demonstrate that long-term suppression of inflammatory activity in MS patients who received HSCT does not depend on persisting lymphopenia and is associated with profound qualitative immunological changes that demonstrate a de novo regeneration of the T cell compartment.

Enhanced lymphocyte proliferation responses in pediatric patients early after myelosuppressive chemotherapy

BACKGROUND

It has long been known that patients both after myelosuppressive chemotherapy (ChTh) and after myeloablative bone marrow transplantation (BMT) show a long lasting impairment of cellular immune functions. However, recent reports have revealed that early after BMT a passing state of augmented immune responsiveness exists. Adoptive T cell therapy in this period of lymphopenia-induced (homeostatic) proliferation has shown better results than in steady state in murine studies.

PROCEDURE

To determine whether also early after myelosuppressive ChTh enhanced immune responses can be found, we have determined proliferation of peripheral blood lymphocytes and calcium influx and performed immunophenotyping in pediatric patients recovering from myelosuppressive ChTh in comparison to immunoreconstituted patients late after BMT.

RESULTS

The lymphocytes of the ChTh patients were found to proliferate vigorously in response to stimulation with a variety of antibodies and mitogens, while in the BMT patients any stimulation was severely reduced. The increase of intracellular calcium after stimulation was similar in both patient groups. ChTh patients showed an expansion of an activated "naive" phenotype (CD45RO- HLA-DR+) in both the CD4 and CD8 subsets. In contrast, BMT patients showed a prominent expansion of "memory type" T lymphocytes (CD45RO+ HLA-DR+).

CONCLUSIONS

Early after ChTh, a period of immunoaugmentation seems to exist. Whether this observation can be used clinically to increase cure rates remains to be elucidated.

HIV-infected children with moderate/severe immune-suppression: changes in the immune system after highly active antiretroviral therapy

The objective of this study was to monitor the changes in the immune system of HIV-infected children with moderate or severe immunodeficiency after highly active antiretroviral therapy (HAART), comprising a follow-up study in 14 HIV-infected children on HAART at two time points separated approximately by 11.8 +/- 0.4 (9.9; 15.4) months. HIV-infected children had significantly lower TREC levels than the control group, but 1 year after HAART the levels increased significantly (P < 0.05). In contrast, viral load (VL) did not change significantly. A positive correlation between T cell receptor excision circle (TREC) levels and both CD4(+) T cell absolute counts (r = 0.558; P = 0.05) and percentages (r = 0.625; P = 0.030) was found. During follow-up on HAART, the percentages and absolute counts of naive CD4(+) and CD8(+) T cell subsets were increased significantly (P < 0.05). CD4(+) CD45RA(hi+) CD62L(+), CD4(+) CD45RA(+) and CD4(+) CD38(+) percentages, and the CD8(+) CD45RA(hi+) CD62L(+) counts reached similar values to the control group. Also, CD8(+) CD45RO(+) CD38(+) and CD8(+) CD45RO(+) percentages, and CD8(+) CD45RO(+) CD38(+) absolute counts (P < 0.05) decreased with respect to the baseline. Lymphoproliferative responses to pokeweed mitogen (PWM) before HAART were lower in HIV-infected children than the control group, but they recovered to normal levels after a year on HAART. Tumour necrosis factor (TNF)-alpha and interferon (IFN)-gamma production by PHA-activated peripheral blood mononuclear cells (PBMC) was lower before HAART (P < 0.001), but reached similar levels to the control group 1 year after HAART. In HIV-infected children IgG, IgG(1) and IgG(3) plasma levels decreased significantly after HAART. The immune system reconstitution induced by HAART in HIV-infected children seems to be the consequence of decreased immune system activation and naive T cell reconstitution, mainly of thymic origin.

Flt3 ligand enhances thymic-dependent and thymic-independent immune reconstitution

Despite recent progress in our understanding of the biology of T-cell homeostasis, clinically available therapies to substantially improve immune reconstitution in patients sustaining T-cell depletion are lacking. T cells are regenerated via a dynamic interplay between thymopoiesis and thymic-independent homeostatic peripheral expansion (HPE). Using athymic mice subjected to T-cell depletion, we observed that HPE is critically dependent on dendritic cells (DCs) for presentation of antigen, raising the possibility that the availability of DCs might be limiting in vivo for HPE to occur efficiently. Indeed, flt3 ligand (flt3L) treatment of athymic mice subjected to T-cell depletion (without DC depletion) substantially enhanced HPE and improved immune competence. Following bone marrow transplantation (BMT) in athymic hosts, both dendritic cells and T cells were profoundly depleted and flt3L therapy restored DC numbers and enhanced HPE. In addition, thymus-bearing BMT recipients treated with flt3L regenerated increased numbers of thymic-dependent progeny with increased numbers of T-cell receptor excision circle (TREC)-positive T cells, indicating increased thymopoiesis. Therefore, flt3L is a potent immunorestorative agent that enhances both thymic-dependent and thymic-independent pathways of T-cell regeneration.

Immune reconstitution

Lymphocyte recovery is delayed following autologous haematopoietic stem cell transplantation (HSCT). B-cells recover before T-cells and CD8+ before CD4+ T-cells. The initial phase of T-cell recovery is dependent upon the expansion of mature host T-cells that have survived conditioning or are transferred back with the graft. This phase is therefore quicker when the graft is not CD34+ selected. Subsequently, naïve T-cells appear. Naïve CD4+ T-cell recovery is thymus dependent and starts at around 6-9 months. Naïve CD8+ recovery occurs earlier and seems less thymus dependent. Immune function recovers later than lymphocyte number, the former being dependent on a broad repertoire and diversity of effector function. We currently do not know which reconstitution markers are more likely to predict prolonged disease remission as opposed to relapse. Similarly, it is unclear whether disease-specific factors influence reconstitution. A continued, close collaboration between scientists and physicians should both improve the outcomes of HSCT and also provide important pathogenic information about the diseases under treatment.

Aging, immunity and cancer

Immunosenescence, the progressive decline in immune function that develops with age, results from cumulative alterations in critical B- and T-cell subpopulations. Decreases in circulating memory B cells and in germinal center formation are evident in the elderly, possibly due to diminished follicular dendritic-cell function. T-cell dysfunction is associated with reduced thymic generation of naïve T cells, virus-induced expansion of terminal effectors and increased levels of memory cells producing type I and II cytokines. The diversity of the T-cell receptor repertoire is diminished by the first two changes, and elevated type I cytokines might contribute to the pro-inflammatory cytokine milieu present in the elderly.

Stem-cell transplantation for autoimmune diseases

The use of intensive immunosuppressive treatment coupled with BM stem-cell transplantation (SCT) to treat human autoimmune diseases (AID) follows anecdotal observations of responses of AID to allogeneic SCT and an extensive background of experience with SCT in animals with AID. In the last decade, numerous clinical trials have been initiated to explore a potential benefit of (mainly autologous) SCT in advanced and debilitating cases of rheumatoid arthritis, scleroderma, systemic lupus erythematosis and multiple sclerosis. In this review the etiology of AID and the experimental basis of SCT is presented, together with recent clinical results of SCT for AID. While much has been learned about the risks and benefits of SCT in AID, the underlying mechanisms regulating remission and relapse of AID after treatment remain largely unknown.

Interleukin-2 immunotherapy exerts a differential effect on CD4 and CD8 T cell dynamics

BACKGROUND

Emerging evidence indicates that CD4 and CD8 T cell recovery is differentially regulated during HIV infection. The hallmark of interleukin-2 (IL-2)-induced immune reconstitution is the selective outgrowth of CD4 through undefined mechanisms.

OBJECTIVE

To delineate the effect of IL-2 on T cell homeostasis by analysing the differential impact of IL-2 immunotherapy on CD4 and CD8 dynamics.

DESIGN

A randomized trial of 15 HIV-positive patients, eight receiving IL-2 immunotherapy with highly active antiretroviral therapy (HAART) and seven with HAART alone. Patients were followed for a 48-week period following three IL-2 cycles (overall, 10 weeks in duration).

METHODS

CD4 and CD8 count, naive and memory immunophenotype, proliferation by Ki67, and CD8+CD38+ activated pattern were measured longitudinally by flow cytometry. Thymic output contribution to both CD4 and CD8 was evaluated by measurement of T cell receptor excision circles (TREC). Wilcoxon test was used to compare results.

RESULTS

Compared with changes seen with HAART alone, IL-2 induced a more significant rise in CD4 than CD8 T cell count (P < 0.01), associated with a significant increase in Ki67-proliferating CD4 (P < 0.05), whereas no changes were seen in CD8+Ki67+ (P > 0.05). Furthermore, IL-2 administration was associated with CD4 TREC increase, whereas CD8 TREC remained stable (P > 0.05). Modifications in CD4 and CD8 T cells seen in patients taking only HAART were not associated with changes in CD4 and CD8 TREC.

CONCLUSIONS

By showing a differential impact on CD4 and CD8 homeostasis, the study suggests that IL-2-associated immune reconstitution results from protean interactions between T cell compartments; this has significant implications for the correct planning of immunotherapeutic strategies.

Selective CD4+ lymphopenia in melanoma patients treated with temozolomide: a toxicity with therapeutic implications

PURPOSE

Standard schedule temozolomide (TMZ; daily for 5 days every 4 weeks) is often used in melanoma patients, but phase III data show that it is no more effective than standard dacarbazine. Extended TMZ dosing regimens may be superior by delivering the drug continuously at a higher dose over time. Using an extended dosing schedule, we noted a high incidence of lymphopenia and occasional opportunistic infections (OIs). Here we report our retrospective experience in the first 97 patients.

MATERIALS AND METHODS

TMZ was administered at 75 mg/m(2)/d orally for 6 weeks every 8 weeks, although nine patients were treated continuously without a break. Seventeen patients were treated with TMZ alone; 73 patients received TMZ with thalidomide; seven patients received TMZ with low-dose interferon alfa.

RESULTS

Median duration of TMZ treatment was 113 days; 29% received > or = 24 weeks of therapy. Lymphopenia was seen in 60% of patients (absolute lymphocyte count < 800/microL) with a median of 101 days to lymphopenia. TMZ did not cause significant neutropenia or thrombocytopenia. Lymphopenia was not more common in patients treated concomitantly with thalidomide. In all patients analyzed for lymphocyte subsets, lymphopenia induced by TMZ affected the CD4(+) compartment preferentially. There were two documented OIs (Pneumocystis and Aspergillus pneumonia) as well as other infections indicative of T-cell dysfunction in another 21 patients.

CONCLUSION

TMZ at this dose and schedule results in CD4(+) lymphopenia in a majority of patients that can result in OIs. Pneumocystis pneumonia prophylaxis should be considered for patients who develop sustained lymphopenia on TMZ.

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.