Thymic aging and T-cell regeneration

Dynamics of T cell repertoire renewal following autologous hematopoietic stem cell transplantation in multiple sclerosis

Autologous hematopoietic stem cell transplantation (aHSCT) is a highly effective treatment of multiple sclerosis (MS). It depletes autoreactive cells and subsequently renews adaptive immune cells. The possible proinflammatory potential of surviving T cells early after aHSCT has not been studied. Here, we examined the dynamics of new and surviving T cells in 27 patients after aHSCT by multidimensional flow cytometry, T cell receptor (TCR) sequencing, specificity testing, telomere length profiling, and HLA genotyping. Early after aHSCT, naïve T cells are barely detectable, whereas effector memory (EM) T cells quickly reconstitute to pre-aHSCT values. EM CD4+T cells early after aHSCT have shorter telomeres, have higher expression of senescence and exhaustion markers, and proliferate less than those before aHSCT. We find a median TCR repertoire overlap of 26% between the early post-aHSCT EM CD4+T cells and pre-aHSCT, indicating persistence of EM CD4+T cells early after transplantation. The EM CD4+TCR repertoire overlap declines to 15% at 12 months after aHSCT, whereas the naïve TCR repertoire entirely renews. HLA-DR–associated EM CD4+T cell reactivity toward MS-related antigens decreased after aHSCT, whereas reactivity toward EBV increased. Our data show substantial survival of pre-aHSCT EM CD4+T cells early after transplantation but complete renewal of the T cell repertoire by nascent T cells later.

Generation of functional human thymic cells from induced pluripotent stem cells

BACKGROUND

The thymus is a glandular organ that is essential for the formation of the adaptive immune system by educating developing T cells. The thymus is most active during childhood and involutes around the time of adolescence, resulting in a severe reduction or absence of naive T-cell output. The ability to generate a patient-derived human thymus would provide an attractive research platform and enable the development of novel cell therapies.

OBJECTIVES

This study sought to systematically evaluate signaling pathways to develop a refined direct differentiation protocol that generates patient-derived thymic epithelial progenitor cells from multiple induced pluripotent stem cells (iPSCs) that can further differentiate into functional patient-derived thymic epithelial cells on transplantation into athymic nude mice.

METHODS

Directed differentiation of iPSC generated TEPs that were transplanted into nude mice. Between 14 and 19 weeks posttransplantation, grafts were removed and analyzed by flow cytometry, quantitative PCR, bulk RNA sequencing, and single-cell RNA sequencing for markers of thymic-cell and T-cell development.

RESULTS

A direct differentiation protocol that allows the generation of patient-derived thymic epithelial progenitor cells from multiple iPSC lines is described. On transplantation into athymic nude mice, patient-derived thymic epithelial progenitor cells further differentiate into functional patient-derived thymic epithelial cells that can facilitate the development of T cells. Single-cell RNA sequencing analysis of iPSC-derived grafts shows characteristic thymic subpopulations and patient-derived thymic epithelial cell populations that are indistinguishable from TECs present in primary neonatal thymus tissue.

CONCLUSIONS

These findings provide important insights and resources for researchers focusing on human thymus biology.

Immune system aging and the aging-related diseases in the COVIID-19 era

The interest in the process of aging, and specifically in how aging affects the working of our immune system, has recently enormously grown among both specialists (immunologists and gerontologists) and representatives of other disciplines of health sciences. An obvious reason for this interest is the current pandemics of COVID-19, known to affect the elderly more than younger people. In this paper current knowledge about mechanisms and complex facets of human immune system aging is presented, stemming from the knowledge about the working of various parts of the immune system, and leading to understanding of immunological mechanisms of chronic, inflammatory, aging-related diseases and of COVID-19.

Interleukin-7 Biology and Its Effects on Immune Cells: Mediator of Generation, Differentiation, Survival, and Homeostasis

Interleukin-7 (IL-7), a molecule known for its growth-promoting effects on progenitors of B cells, remains one of the most extensively studied cytokines. It plays a vital role in health maintenance and disease prevention, and the congenital deficiency of IL-7 signaling leads to profound immunodeficiency. IL-7 contributes to host defense by regulating the development and homeostasis of immune cells, including T lymphocytes, B lymphocytes, and natural killer (NK) cells. Clinical trials of recombinant IL-7 have demonstrated safety and potent immune reconstitution effects. In this article, we discuss IL-7 and its functions in immune cell development, drawing on a substantial body of knowledge regarding the biology of IL-7. We aim to answer some remaining questions about IL-7, providing insights essential for designing new strategies of immune intervention.

The Impact of Graft CD3 Cell/Regulatory T Cell Ratio on Acute Graft-versus-Host Disease and Post-Transplantation Outcome: A Prospective Multicenter Study of Patients with Acute Leukemia Undergoing Allogeneic Peripheral Blood Stem Cell Transplantation

Although it is well known that tumor site- or bone marrow-infiltrating regulatory T cells (Tregs) might be correlated with worse outcomes in solid tumors and acute leukemias by promoting immune surveillance escape, their contribution to the immediate post-allogeneic transplantation phase by peripheral blood (PB) allografts remains unclear. Moreover, the Treg content in stem cells harvested from PB has been suggested to be correlated with acute graft versus-host-disease (aGVHD) and immunologic recovery after allogeneic PB stem cell transplantation (allo-PBSCT). This study aimed to investigate the impact of the graft content of Tregs, as graft CD3⁺/Tregs ratio (gCD3/TregsR), on acute GVHD and post-allo-PBSCT outcomes. We prospectively enrolled 94 consecutive patients at 9 Italian centers of the Gruppo Italiano Trapianto di Midollo Osseo (GITMO) with acute myelogenous (n = 71; 75%) or lymphoblastic (n = 23; 25%) leukemia in complete remission who underwent matched related donor (n = 35; 37%) or unrelated donor (n = 59; 63%) allo-PBSCT. The median graft CD3⁺ cell, Treg, and gCD3/TregsR values were 196 × 10⁶/kg body weight (range, 17 to 666 × 10⁶/kg), 3 × 10⁶/kg (range, 0.1 to 35 × 10⁶/kg), and 71 (range, 1 to 1883), respectively. The discriminatory power of the gCD3/TregsR value to predict grade ≥II aGVHD was assessed by estimating the area under the receiver operating characteristic (ROC) curve (AUC). Any grade and grade ≥II aGVHD occurred in 24 (26%) and 17 (18%) allo-PBSCT recipients, respectively. By ROC analysis, AUC (0.74; 95% confidence interval [CI], 0.608 to 0.866; P = .002) identified 70 as the optimal gCD3/TregsR cutoff value predicting the appearance of grade ≥II aGVHD with 76% sensitivity and 71% specificity. Patients were subdivided into a high (ROC curve value ≥70) gCD3/TregsR group (HR; n = 48) and a low (ROC curve value <70) gCD3/TregsR group (LR; n = 46). The incidence of grade II-IV aGVHD was lower in the LR group compared with the HR group (9% [4 of 46] versus 27% [13 of 48]) in both univariate analysis (odds ratio [OR], 4.8; 95% CI, 1.44 to 16.17; P = .015) and multivariate analysis (OR, 5.0; 95% CI, 1.34 to 18.93; P = .017), whereas no differences were documented taking into account aGVHD of any grade. The overall survival, disease-free survival, nonrelapse mortality, and relapse rates at 2 and 3 years were 61% and 54%, 62% and 55%, 15% and 23%, and 27% and 30%, respectively. Of note, gCD3/TregsR did not significantly correlate with relapse (P = .135). Taken together, our data from this prospective multicenter study confirm the value of Tregs in preventing aGVHD while maintaining the graft-versus-leukemia effect. © 2021 American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc.

STING Ligand-Mediated Priming of Functional CD8+ T Cells Specific for HIV-1-Protective Epitopes from Naive T Cells

Functional HIV-1-specific CD8+ T cells primed from naive T cells are expected to act as effector T cells in a "shock-and-kill" therapeutic strategy for an HIV-1 cure since less functional HIV-1-specific CD8+ T cells are elicited from memory T cells in HIV-1-infected individuals on combined antiretroviral therapy (cART). CD8+ T cells specific for HIV-1 conserved and protective epitopes are candidates for such T cells. We investigated the priming with STING ligand of CD8+ T cells specific for HLA-B*52:01 or HLA-C*12:02-restricted protective epitopes from naive T cells. STING ligand 3'3'-cGAMP effectively primed CD8+ T cells specific for 3 of 4 HLA-B*52:01-restricted epitopes but failed to prime those specific for all 3 HLA-C*12:02-restricted epitopes from the naive T cells of HIV-1-uninfected individuals having an HLA-B*52:01-C*12:02 protective haplotype. These HLA-B*52:01-restricted CD8+ T cells had a strong ability to suppress HIV-1 replication and expressed a high level of cytolytic effector molecules. The viral suppression ability of these T cells was significantly correlated with the expression level of perforin and showed a trend for a positive correlation with the expression level of CD107a. The present study highlighted the priming with STING ligand of functional CD8+ T cells specific for protective epitopes, which T cells would contribute as effector T cells to a shock-and-kill therapy. IMPORTANCE The current "shock-and-kill" therapeutic strategy for HIV cure has been directed toward eliminating latent viral reservoirs by reactivation of latent reservoirs with latency-reversing agents followed by eradication of these cells by immune-mediated responses. Although HIV-1-specific T cells are expected to eradicate viral reservoirs, the function of these T cells is reduced in HIV-1-infected individuals with long-term cART. Therefore, priming of HIV-1-specific T cells with high function from naive T cells is to be expected in these individuals. In this study, we demonstrated the priming with STING ligand 3'3'-cGAMP of CD8+ T cells specific for HIV-1-protective epitopes from naive T cells. cGAMP primed CD8+ T cells specific for 3 HLA-B*52:01-restricted protective epitopes, which cells expressed a high level of cytolytic effector molecules and effectively suppressed HIV-1 replication. The present study suggested that the priming with STING ligand of functional CD8+ T cells specific for protective epitopes would be useful in a therapy for an HIV-1 cure.

Immune reconstitution and infectious complications following axicabtagene ciloleucel therapy for large B-cell lymphoma

Chimeric antigen receptor (CAR) T-cell therapy targeting CD19 has significantly improved outcomes in the treatment of refractory or relapsed large B-cell lymphoma (LBCL). We evaluated the long-term course of hematologic recovery, immune reconstitution, and infectious complications in 41 patients with LBCL treated with axicabtagene ciloleucel (axi-cel) at a single center. Grade 3+ cytopenias occurred in 97.6% of patients within the first 28 days postinfusion, with most resolved by 6 months. Overall, 63.4% of patients received a red blood cell transfusion, 34.1% of patients received a platelet transfusion, 36.6% of patients received IV immunoglobulin, and 51.2% of patients received growth factor (granulocyte colony-stimulating factor) injections beyond the first 28 days postinfusion. Only 40% of patients had recovered detectable CD19+ B cells by 1 year, and 50% of patients had a CD4+ T-cell count <200 cells per μL by 18 months postinfusion. Patients with durable responses to axi-cel had significantly longer durations of B-cell aplasia, and this duration correlated strongly with the recovery of CD4+ T-cell counts. There were significantly more infections within the first 28 days compared with any other period of follow-up, with the majority being mild-moderate in severity. Receipt of corticosteroids was the only factor that predicted risk of infection in a multivariate analysis (hazard ratio, 3.69; 95% confidence interval, 1.18-16.5). Opportunistic infections due to Pneumocystis jirovecii and varicella-zoster virus occurred up to 18 months postinfusion in patients who prematurely discontinued prophylaxis. These results support the use of comprehensive supportive care, including long-term monitoring and antimicrobial prophylaxis, beyond 12 months after axi-cel treatment.

Neurological Complications Associated with the Blood-Brain Barrier Damage Induced by the Inflammatory Response During SARS-CoV-2 Infection

The main discussion above of the novel pathogenic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has focused substantially on the immediate risks and impact on the respiratory system; however, the effects induced to the central nervous system are currently unknown. Some authors have suggested that SARS-CoV-2 infection can dramatically affect brain function and exacerbate neurodegenerative diseases in patients, but the mechanisms have not been entirely described. In this review, we gather information from past and actual studies on coronaviruses that informed neurological dysfunction and brain damage. Then, we analyzed and described the possible mechanisms causative of brain injury after SARS-CoV-2 infection. We proposed that potential routes of SARS-CoV-2 neuro-invasion are determinant factors in the process. We considered that the hematogenous route of infection can directly affect the brain microvascular endothelium cells that integrate the blood-brain barrier and be fundamental in initiation of brain damage. Additionally, activation of the inflammatory response against the infection represents a critical step on injury induction of the brain tissue. Consequently, the virus' ability to infect brain cells and induce the inflammatory response can promote or increase the risk to acquire central nervous system diseases. Here, we contribute to the understanding of the neurological conditions found in patients with SARS-CoV-2 infection and its association with the blood-brain barrier integrity.

Quantifying circulating Th17 cells by qPCR: potential as diagnostic biomarker for rheumatoid arthritis

OBJECTIVE

The diagnosis of RA patients remains a challenge, especially in ACPA-negative disease. Novel T-cell subsets, particularly Th17 may be useful, although data on Th17 frequency using flow cytometry in RA are conflicting. We investigated whether a novel epigenetic qPCR assay for the quantification of Th17 could differentiate patients with RA from those with symptoms evolving towards an alternative diagnosis.

METHODS

We used a qPCR assay measuring the extent of the methylation at a key position in the IL-17 and CD4 genes. Assays were performed on whole blood from 49 healthy controls (HC) and 165 early arthritis clinic patients. Flow cytometry was further used to detect the expression of CXCR4 on Th17 cells.

RESULTS

In 75 inflammatory arthritis patients who progressed to RA, the qPCR assays showed significantly fewer Th17 cells compared with 90 patients who did not (P<0.0001). Regression models demonstrated a high predictive value for RA development (75.8% correct prediction), and particularly for the ACPA-negative group (n = 125) where Th17 and swollen joint count (SJC) were the only predictors (73% correct prediction). The chemokine receptor CXCR4 had significantly higher expression on Th17 from early RA patients (n = 11) compared with HC (n = 15).

CONCLUSION

The results of the epigenetic qPCR assay showed that low levels of Th17 cells were predictive of developing RA, particularly in the ACPA-negative patients. This could have value for insights into pathogenesis and management. The results suggest the recruitment of Th17 to the inflammatory disease site, consistent with high CXCR4 expression.

Single-Cell Transcriptomics of Human Mesenchymal Stem Cells Reveal Age-Related Cellular Subpopulation Depletion and Impaired Regenerative Function

Although bone marrow-derived mesenchymal stem cells (BM-MSCs) are widely recognized as promising therapeutic agents, the age-related impacts on cellular function remain largely uncharacterized. In this study, we found that BM-MSCs from young donors healed wounds in a xenograft model faster compared with their aged counterparts (p < .001). Given this significant healing advantage, we then used single-cell transcriptomic analysis to provide potential molecular insights into these observations. We found that the young cells contained a higher proportion of cells characterized by a higher expression of genes involved in tissue regeneration. In addition, we identified a unique, quiescent subpopulation that was exclusively present in young donor cells. Together, these findings may explain a novel mechanism for the enhanced healing capacity of young stem cells and may have implications for autologous cell therapy in the extremes of age. Stem Cells 2019;37:240-246.

Aging of lymphoid organs: Can photobiomodulation reverse age-associated thymic involution via stimulation of extrapineal melatonin synthesis and bone marrow stem cells?

Thymic atrophy and the subsequent reduction in T-cell production are the most noticeable age-related changes affecting lymphoid organs in the immune system. In fact, thymic involution has been described as "programmed aging." New therapeutic approaches, such as photobiomodulation (PBM), may reduce or reverse these changes. PBM (also known as low-level laser therapy) involves the delivery of non-thermal levels of red or near-infrared light that are absorbed by mitochondrial chromophores, in order to prevent tissue death and stimulate healing and regeneration. PBM may reverse or prevent thymic involution due to its ability to induce extrapineal melatonin biosynthesis via cyclic adenosine monophosphate (AMP) or NF-kB activation, or alternatively by stimulating bone marrow stem cells that can regenerate the thymus. This perspective puts forward a hypothesis that PBM can alter thymic involution, improve immune functioning in aged people and even extend lifespan.

The Bioelectric Code: Reprogramming Cancer and Aging From the Interface of Mechanical and Chemical Microenvironments

Cancer is a complex, heterogeneous group of diseases that can develop through many routes. Broad treatments such as chemotherapy destroy healthy cells in addition to cancerous ones, but more refined strategies that target specific pathways are usually only effective for a limited number of cancer types. This is largely due to the multitude of physiological variables that differ between cells and their surroundings. It is therefore important to understand how nature coordinates these variables into concerted regulation of growth at the tissue scale. The cellular microenvironment might then be manipulated to drive cells toward a desired outcome at the tissue level. One unexpected parameter, cellular membrane voltage (Vm), has been documented to exert control over cellular behavior both in culture and in vivo. Manipulating this fundamental cellular property influences a remarkable array of organism-wide patterning events, producing striking outcomes in both tumorigenesis as well as regeneration. These studies suggest that Vm is not only a key intrinsic cellular property, but also an integral part of the microenvironment that acts in both space and time to guide cellular behavior. As a result, there is considerable interest in manipulating Vm both to treat cancer as well as to regenerate organs damaged or deteriorated during aging. However, such manipulations have produced conflicting outcomes experimentally, which poses a substantial barrier to understanding the fundamentals of bioelectrical reprogramming. Here, we summarize these inconsistencies and discuss how the mechanical microenvironment may impact bioelectric regulation.

Persistent changes in circulating white blood cell populations after splenectomy

The effect of splenectomy on the incidence of infections and thromboembolisms has been investigated thoroughly. Nevertheless, the long-term effects of splenectomy on immunological profile and circulating blood counts have not been described before. To study such long-term effects, we analysed several parameters in splenectomised trauma patients and compared the results of this group ("otherwise healthy patients") to patients with a specific underlying disease. We measured platelet count, leukocytes and differential, lymphocyte subsets, serum levels of immunoglobulins, and complement pathways in 113 patients. Indications to perform a splenectomy were trauma (n = 42), Hodgkin lymphoma (n = 24), hereditary spherocytosis (n = 21), and immune thrombocytopenia (n = 26). In trauma patients lymphocytes and lymphocytes subsets were particularly elevated compared to normal population values. Splenectomised patients with Hodgkin lymphoma had significant lower numbers of T lymphocytes than trauma patients. Significant increases in platelets, leukocytes, and monocytes were observed in patients with hereditary spherocytosis. Occurrence of MBL genotype was different in ITP patients than in other splenectomised groups and the normal population. In splenectomised patients (> 4 years), platelet counts and lymphocyte subsets are increased which persist over time. As a result, these blood counts in splenectomised patients differ from reference values in the normal population.

Role of neuroinflammation in neurodegeneration: new insights

Previously, the contribution of peripheral infection to cognitive decline was largely overlooked however, the past 15 years have established a key role for infectious pathogens in the progression of age-related neurodegeneration. It is now accepted that the immune privilege of the brain is not absolute, and that cells of the central nervous system are sensitive to both the inflammatory events occurring in the periphery and to the infiltration of peripheral immune cells. This is particularly relevant for the progression of Alzheimer’s disease, in which it has been demonstrated that patients are more vulnerable to infection-related cognitive changes. This can occur from typical infectious challenges such as respiratory tract infections, although a number of specific viral, bacterial, and fungal pathogens have also been associated with the development of the disease. To date, it is not clear whether these microorganisms are directly related to Alzheimer’s disease progression or if they are opportune pathogens that easily colonize those with dementia and exacerbate the ongoing inflammation observed in these individuals. This review will discuss the impact of each of these challenges, and examine the changes known to occur with age in the peripheral immune system, which may contribute to the age-related vulnerability to infection-induced cognitive decline.

Next generation HLA-haploidentical HSCT

Relapse is still the major cause of failure of allogeneic stem cell transplantation in high-risk acute leukemia patients. Indeed, whoever the donor and whatever the transplantation strategy, post-transplant relapse rates are ~30%, which is hardly satisfactory. The present phase 2 study analyzed the impact of adoptive immunotherapy with naturally occurring FoxP3+ T-regulatory cells (2 × 10(6) per kg) and conventional T lymphocytes (1 × 10(6) per kg) on prevention of GvHD and leukemia relapse in 43 high-risk adults undergoing full-haplotype mismatched transplantation without any post-transplant immunosuppression. Ninety-five percent of patients achieved full-donor type engraftment. Only 6/41 patients (15%) developed ⩾ grade II acute GvHD. Specific CD4(+) and CD8(+) for opportunistic pathogens emerged significantly earlier than after standard T-cell-depleted haplo-transplantation. The probability of disease-free survival was 0.56. At a median follow-up of 46 months (range 18-65 months), only 2/41 evaluable patients have relapsed. The cumulative incidence of relapse was significantly lower than in historical controls (0.05 vs 0.21; P = 0.03). These results demonstrate that the immunosuppressive potential of Tregs can be used to suppress GvHD without loss of the benefits of GvL activity. Humanized murine models provided insights into the mechanisms underlying separation of GvL from GvHD.

Neonatal thymectomy reveals differentiation and plasticity within human naive T cells

The generation of naive T cells is dependent on thymic output, but in adults, the naive T cell pool is primarily maintained by peripheral proliferation. Naive T cells have long been regarded as relatively quiescent cells; however, it was recently shown that IL-8 production is a signatory effector function of naive T cells, at least in newborns. How this functional signature relates to naive T cell dynamics and aging is unknown. Using a cohort of children and adolescents who underwent neonatal thymectomy, we demonstrate that the naive CD4+ T cell compartment in healthy humans is functionally heterogeneous and that this functional diversity is lost after neonatal thymectomy. Thymic tissue regeneration later in life resulted in functional restoration of the naive T cell compartment, implicating the thymus as having functional regenerative capacity. Together, these data shed further light on functional differentiation within the naive T cell compartment and the importance of the thymus in human naive T cell homeostasis and premature aging. In addition, these results affect and alter our current understanding on the identification of truly naive T cells and recent thymic emigrants.

Prolongevity hormone FGF21 protects against immune senescence by delaying age-related thymic involution

Age-related thymic degeneration is associated with loss of naïve T cells, restriction of peripheral T-cell diversity, and reduced healthspan due to lower immune competence. The mechanistic basis of age-related thymic demise is unclear, but prior evidence suggests that caloric restriction (CR) can slow thymic aging by maintaining thymic epithelial cell integrity and reducing the generation of intrathymic lipid. Here we show that the prolongevity ketogenic hormone fibroblast growth factor 21 (FGF21), a member of the endocrine FGF subfamily, is expressed in thymic stromal cells along with FGF receptors and its obligate coreceptor, βKlotho. We found that FGF21 expression in thymus declines with age and is induced by CR. Genetic gain of FGF21 function in mice protects against age-related thymic involution with an increase in earliest thymocyte progenitors and cortical thymic epithelial cells. Importantly, FGF21 overexpression reduced intrathymic lipid, increased perithymic brown adipose tissue, and elevated thymic T-cell export and naïve T-cell frequencies in old mice. Conversely, loss of FGF21 function in middle-aged mice accelerated thymic aging, increased lethality, and delayed T-cell reconstitution postirradiation and hematopoietic stem cell transplantation (HSCT). Collectively, FGF21 integrates metabolic and immune systems to prevent thymic injury and may aid in the reestablishment of a diverse T-cell repertoire in cancer patients following HSCT.

Young, proliferative thymic epithelial cells engraft and function in aging thymuses

The thymus reaches its maximum size early in life and then begins to shrink, producing fewer T cells with increasing age. This thymic decline is thought to contribute to age-related T cell lymphopenias and hinder T cell recovery after bone marrow transplantation. Although several cellular and molecular processes have been implicated in age-related thymic involution, their relative contributions are not known. Using heterochronic parabiosis, we observe that young circulating factors are not sufficient to drive regeneration of the aged thymus. In contrast, we find that resupplying young, engraftable thymic epithelial cells (TECs) to a middle-aged or defective thymus leads to thymic growth and increased T cell production. Intrathymic transplantation and in vitro colony-forming assays reveal that the engraftment and proliferative capacities of TECs diminish early in life, whereas the receptivity of the thymus to TEC engraftment remains relatively constant with age. These results support a model in which thymic growth and subsequent involution are driven by cell-intrinsic changes in the proliferative capacity of TECs, and further show that young TECs can engraft and directly drive the growth of involuted thymuses.

“Designed” grafts for HLA-haploidentical stem cell transplantation

Today human leukocyte antigen-haploidentical transplantation is a feasible option for patients with high-risk acute leukemia who do not have matched donors. Whether it is T-cell replete or T-cell depleted, it is still, however, associated with issues of transplant-related mortality and posttransplant leukemia relapse. After reports that adoptive immunotherapy with T-regulatory cells controls the alloreactivity of conventional T lymphocytes in animal models, tomorrow’s world of haploidentical transplantation will focus on new “designed” grafts. They will contain an appropriate ratio of conventional T lymphocytes and T-regulatory cells, natural killer cells, γ δ T cells, and other accessory cells. Preliminary results of ongoing clinical trials show the approach is feasible. It is associated with better immune reconstitution and a quite powerful graft-versus-leukemia effect with a low incidence of graft-versus-host disease and no need for posttransplant pharmacological prophylaxis. Future strategies will focus on enhancing the clinical benefit of T-regulatory cells by increasing their number and strengthening their function.

Methods of detection of immune reconstitution and T regulatory cells by flow cytometry

Allogeneic hematopoietic stem cell therapy (HSCT) remains one of the few curative treatments for high-risk hematological malignancies (high-risk leukemia, myelodysplastic syndromes, advanced myeloproliferative disorders, high-risk lymphomas, and multiple myeloma) and is currently applied in more than 15,000 patients per year in Europe. Following HSCT, patients experience a period of reconstitution of the immune system, which seems to be highly dependent on conditioning, immunosuppression regimes, and the level of adverse events the patients experience. During this reconstitution period, the patient is immune compromised and susceptible to opportunistic infections and disease relapse. Consequently, a large number of clinical studies have been devoted to monitoring the recovery of the immune system following HSCT in the hopes of determining which cellular subsets are indicative of a favorable outcome. In this chapter we review the methods that have been employed to monitor the immune reconstitution and what clinical observations have been made. Of particular interest is the regulatory T cell (Treg) subset, which has been associated with tolerance and has been the subject of recent clinical trials as a possible cellular therapy for rejection reactions. Finally we will detail a proposed methodology for the flow cytometric assessment of cellular reconstitution post-HSCT.

Immunosenescence and immune response in organ transplantation

The immune system undergoes a complex and continuous remodeling with aging. Immunosenescence results into both quantitative and qualitative changes of specific cellular subpopulations that have major impact on allorecognition and alloresponse, and consequently on graft rejection and tolerance. Here, we are going to review the immunological changes associated with the aging process relevant for transplantation. Interventions to selectively target changes associated with the senescence process seem promising therapeutic strategies to improve transplantation outcome.

Immunosenescence and organ transplantation

Increasing numbers of elderly transplant recipients and a growing demand for organs from older donors impose pressing challenges on transplantation medicine. Continuous and complex modifications of the immune system in parallel to aging have a major impact on transplant outcome and organ quality. Both, altered alloimmune responses and increased immunogenicity of organs present risk factors for inferior patient and graft survival. Moreover, a growing body of knowledge on age-dependent modifications of allorecognition and alloimmune responses may require age-adapted immunosuppression and organ allocation. Here, we summarize relevant aspects of immunosenescence and their possible clinical impact on organ transplantation.

Interpreting Stress Responses during Routine Toxicity Studies

Stress often occurs during toxicity studies. The perception of sensory stimuli as stressful primarily results in catecholamine release and activation of the hypothalamic–pituitary–adrenal (HPA) axis to increase serum glucocorticoid concentrations. Downstream effects of these neuroendocrine signals may include decreased total body weights or body weight gain; food consumption and activity; altered organ weights (e.g., thymus, spleen, adrenal); lymphocyte depletion in thymus and spleen; altered circulating leukocyte counts (e.g., increased neutrophils with decreased lymphocytes and eosinophils); and altered reproductive functions. Typically, only some of these findings occur in a given study. Stress responses should be interpreted as secondary (indirect) rather than primary (direct) test article–related findings. Determining whether effects are the result of stress requires a weight-of-evidence approach. The evaluation and interpretation of routinely collected data (standard in-life, clinical pathology, and anatomic pathology endpoints) are appropriate and generally sufficient to assess whether or not changes are secondary to stress. The impact of possible stress-induced effects on data interpretation can partially be mitigated by toxicity study designs that use appropriate control groups (e.g., cohorts treated with vehicle and subjected to the same procedures as those dosed with test article), housing that minimizes isolation and offers environmental enrichment, and experimental procedures that minimize stress and sampling and analytical bias.

This article is a comprehensive overview of the biological aspects of the stress response, beginning with a Summary (Section 1) and an Introduction (Section 2) that describes the historical and conventional methods used to characterize acute and chronic stress responses. These sections are followed by reviews of the primary systems and parameters that regulate and/or are influenced by stress, with an emphasis on parameters evaluated in toxicity studies: In-life Procedures (Section 3), Nervous System (Section 4), Endocrine System (Section 5), Reproductive System (Section 6), Clinical Pathology (Section 7), and Immune System (Section 8). The paper concludes (Section 9) with a brief discussion on Minimizing Stress-Related Effects (9.1.), and a final section explaining why Parameters routinely measured are appropriate for assessing the role of stress in toxicology studies (9.2.).

Understanding the immune response to seasonal influenza vaccination in older adults: a systems biology approach

Annual vaccination against seasonal influenza is recommended to decrease disease-related mortality and morbidity. However, one population that responds suboptimally to influenza vaccine is adults over the age of 65 years. The natural aging process is associated with a complex deterioration of multiple components of the host immune system. Research into this phenomenon, known as immunosenescence, has shown that aging alters both the innate and adaptive branches of the immune system. The intricate mechanisms involved in immune response to influenza vaccine, and how these responses are altered with age, have led us to adopt a more encompassing systems biology approach to understand exactly why the response to vaccination diminishes with age. Here, the authors review what changes occur with immunosenescence, and some immunogenetic factors that influence response, and outline the systems biology approach to understand the immune response to seasonal influenza vaccination in older adults.

Cord blood T cells retain early differentiation phenotype suitable for immunotherapy after TCR gene transfer to confer EBV specificity

Adoptive T cell therapy can be effective for Epstein-Barr virus (EBV)-associated posttransplant lymphoproliferative disease and melanoma. Transducing high-affinity TCR genes into T lymphocytes is an emerging method to improve potency and specificity of tumor-specific T cells. However, both methods necessitate in vitro lymphocyte proliferation, generating highly differentiated effector cells that display reduced survival and antitumor efficacy postinfusion. TCR-transduction of naive lymphocytes isolated from peripheral blood is reported to provide superior in vivo survival and function. We utilized cord blood (CB) lymphocytes, which comprise mainly naive cells, for transducing EBV-specific TCR. Comparable TCR expression was achieved in adult and CB cells, but the latter expressed an earlier differentiation profile. Further antigen-driven stimulation skewed adult lymphocytes to a late differentiation phenotype associated with immune exhaustion. In contrast, CB T cells retained a less differentiated phenotype after antigen stimulation, remaining CD57-negative but were still capable of antigen-specific polyfunctional cytokine expression and cytotoxicity in response to EBV antigen. CB T cells also retained longer telomeres and in general possessed higher telomerase activity indicative of greater proliferative potential. CB lymphocytes therefore have qualities indicating prolonged survival and effector function favorable to immunotherapy, especially in settings where donor lymphocytes are unavailable such as in solid organ and CB transplantation.

Outcome of allogeneic peripheral blood stem cell transplantation by donor graft CD3+/Tregs ratio: a single-center experience

The therapeutic efficacy of allogeneic peripheral blood stem cell transplantation (PBSCT) for hematological malignancies relies largely on the graft-versus-leukemia (GVL) effects exerted by the donor CD3 cells, but there is a risk of onset of uncontrolled graft-versus-host disease (GVHD). Regulatory T cells (Tregs) (CD4+CD25(high) Foxp3+) are believed to maintain tolerance and to inhibit acute GVHD (aGVHD) after allogeneic PBSCT. Nevertheless, when looking at post-allotransplantation patient outcomes, although the impact of aGVHD on survival is amply documented, so far there is no evidence that the donor graft CD3/Tregs ratio may affect overall survival (OS), nonrelapse mortality (NRM), disease-free survival (DFS), and relapse rates. Our aim was to study the possible impact of the gCD3/Tregs ratio on survival after myeloablative allogeneic PBSCT. We analyzed 74 consecutive patients diagnosed with acute myeloid leukemia (n = 62), acute lymphoblastic leukemia (n = 10), and chronic myeloid leukemia (n = 2) who underwent transplantation with unmanipulated PBSCs from a human leukocyte antigen-identical related donor (n = 48) or a human leukocyte antigen-identical unrelated donor (n = 26). Patients were subdivided into a high gCD3/Tregs ratio (≥36) group (HR group, n = 30) and a low gCD3/Tregs ratio (<36) group (LR group, n = 44). The OS, DFS, NRM, and relapse rates at 3 years were 53%, 51%, 29%, and 34%, respectively. Comparing the LR and HR groups, a statistically significant difference was demonstrated for the 3-year OS, DFS, and NRM rates (65% vs 31%, P = .0001; 67 versus 26%, P = .0001; 5% versus 71%, P < .0001, respectively) but not for relapse (30% vs 25%, P = ns). By multivariate analysis, LR significantly predicted better OS (P = .019), DFS (P = .003), and NRM (P = .05), whereas there was no statistically significant association between LR and relapse (P = .155). Overall, our data may suggest that LR preserves GVL effects but is also protective against aGVHD in allotransplantation patients.

CD3+/Tregs ratio in donor grafts is linked to acute graft-versus-host disease and immunologic recovery after allogeneic peripheral blood stem cell transplantation

Graft-versus-host disease (GVHD), mediated by mature T cells present in the donor graft, remains a major complication after allogeneic peripheral blood stem cell transplantation (PBSCT). Regulatory T cells (Tregs) (CD4(+)CD25(high)Foxp3(+)) are believed to maintain tolerance and to inhibit GVHD after allogeneic PBSCT (allo-PBSCT). In this study, we analyzed the graft CD3(+)/Tregs ratio (gCD3/Tregs R) and evaluated its impact on acute GVHD (aGVHD) and immunologic recovery after myeloablative allo-PBSCT. We analyzed 65 consecutive patients who underwent transplantation with unmanipulated peripheral blood stem cells from an HLA-identical related donor (n = 45) or an HLA-identical unrelated donor (n = 20). The median CD3(+) and Tregs doses administered were 256 × 10(6)/kg of body weight (range, 67-550 × 10(6)/kg) and 12 × 10(6)/kg (range, 2-21 × 10(6)/kg), respectively; the median gCD3/Tregs R value was 18 (range, 8-250). Patients were subdivided into a high gCD3/Tregs R (≥36) group (HR; n = 26) and a low gCD3/Tregs R (<36) group (LR; n = 39). The incidence of aGVHD (grade II-IV) was lower in the LR group compared with the HR group (8/39 [20%] versus 22/26 [84%]; P < .001). Median cytomegalovirus-specific CD8(+) T lymphocytes were significantly higher in the LR group than in the HR group at 1 month (2 cells/μL versus 0 cells/μL; P < .001), 2 months (6 cells/μL versus 1 cell/μL; P < .001), and 3 months (15 cells/μL versus 3 cells/μL; P < .001) months. Moreover, cytomegalovirus infection/disease was observed in 15% of patients in the LR group versus 69% of patients in the HR group (P < .001). At multivariate logistic regression, gCD3/Tregs R was correlated both with aGVHD (odds ratio, 2.50; 95% confidence interval, 1.30-4.50; P = .05) and with cytomegalovirus infection/disease (odds ratio, 2.35; 95% confidence interval, 0.9-5.00; P = .05). Taken together, our data may suggest that the balance in favor of graft Tregs content is able to mediate protective effects against aGVHD and to maintain an optimal microenviroment for the reconstitution of functional immunity.

Immune profile of pediatric renal transplant recipients following alemtuzumab induction

The incidence of developing circulating anti-human leukocyte antigen antibodies and the kinetics of T cell depletion and recovery among pediatric renal transplant recipients who receive alemtuzumab induction therapy are unknown. In a collaborative endeavor to minimize maintenance immunosuppression in pediatric renal transplant recipients, we enrolled 35 participants from four centers and treated them with alemtuzumab induction therapy and a steroid-free, calcineurin-inhibitor-withdrawal maintenance regimen. At 3 months after transplant, there was greater depletion of CD4(+) than CD8(+) T cells within the total, naive, memory, and effector memory subsets, although depletion of the central memory subset was similar for CD4(+) and CD8(+) cells. Although CD8(+) T cells recovered faster than CD4(+) subsets overall, they failed to return to pretransplant levels by 24 months after transplant. There was no evidence for greater recovery of either CD4(+) or CD8(+) memory cells than naïve cells. Alemtuzumab relatively spared CD4(+)CD25(+)FoxP3(+) regulatory T cells, resulting in a rise in their numbers relative to total CD4(+) cells and a ratio that remained at least at pretransplant levels throughout the study period. Seven participants (20%) developed anti-human leukocyte antigen antibodies without adversely affecting allograft function or histology on 2-year biopsies. Long-term follow-up is underway to assess the potential benefits of this regimen in children.

Multivariate analysis of the relation between immune dysfunction and treatment intensity in children with acute lymphoblastic leukemia

BACKGROUND

Immunoreconstitution following childhood acute lymphoblastic leukemia (ALL) is a complex process during which various immune functions recover differentially. This process is difficult to elucidate since variables are interrelated and require simultaneous evaluation, rendering conventional statistical methods inappropriate.

PROCEDURE

We used principal components analysis (PCA) and projection of latent structures (PLS) to evaluate immune competence in 32 children treated for ALL. One or 6 months after completion of therapy, the relation between lymphocyte subpopulations, lymphocyte function and response to vaccination with tetanus, diphtheria and hemophilus influenzae, was investigated.

RESULTS

PCA demonstrated that increasing treatment intensity correlated with progressive immune dysfunction. Children treated with high intensity had poor response to vaccination associated with loss of humoral memory, decreased CD4(+) 45RA(+) T-lymphocytes and increased CD5+ B-lymphocytes. Patients treated with intermediate intensity had better preservation of humoral memory but decreased CD4(+) 45RA(+) T-cells. Patients with a low intensity regimen had similar vaccination response and lymphocyte levels as controls.

CONCLUSIONS

Our findings demonstrate the utility of PCA and PLS in detecting hidden structures in complex data and suggest that, even 6 months after therapy, patients treated with intermediate and high intensity have attenuated responses to de novo antigens whereas those with high intensity also respond poorly to recall antigens.

Greater than the sum of their parts: combination strategies for immune regeneration following allogeneic hematopoietic stem cell transplantation

Cytoreductive conditioning regimes designed to allow for successful allogeneic hematopoietic stem cell transplantation (allo-HSCT) paradoxically are also detrimental to recovery of the immune system in general but lymphopoiesis in particular. Post-transplant immune depletion is particularly striking within the T cell compartment which is exquisitely sensitive to negative regulation, evidenced by the profound decline in thymic function with age. As a consequence, regeneration of the immune system remains a significant unmet clinical need. Over the past decade studies have revealed several promising therapeutic strategies to address ineffective lymphopoiesis and post-transplant immune deficiency. These include the use of cytokines such as IL-7, IL-12 and IL-15; growth factors and hormones like keratinocyte growth factor (KGF), insulin-like growth factor (IGF)-1 and growth hormone (GH); adoptive transfer of ex vivo-generated precursor T cells (pre-T) and sex steroid ablation (SSA). Moreover, recently several novel approaches have been proposed to generate whole thymii ex vivo using stem cell technologies and bioscaffolds. Increasingly, however, when transferred to the clinic, these strategies alone are not sufficient to restore thymopoiesis in all patients leading to the potential of combination strategies as a way to reign in non-responders. Synergistic enhancement in combination may be due to differential targets may therefore be effective in improving clinical outcomes in the transplant settings as well as in other lymphopenic states induced by high dose chemotherapy/radiation therapy or HIV, and may also be useful in improving responses to vaccination and augmenting anti-tumor immunotherapy.

Immune reconstitution is preserved in hematopoietic stem cell transplantation coadministered with regulatory T cells for GVHD prevention

Recipient-specific regulatory T cells (rsTreg) can prevent graft-versus-host disease (GVHD) by inhibiting donor T-cell expansion after hematopoietic stem cell transplantation (HSCT) in mice. Importantly, in adult humans, because of thymus involution, immune reconstitution during the first months after HSCT relies on the peripheral expansion of donor T cells initially present in the graft. Therefore, we developed a mouse model of HSCT that excludes thymic output to study the effect of rsTreg on immune reconstitution derived from postthymic mature T cells present within the graft. We showed that GVHD prevention with rsTreg was associated with improvement of the limited immune reconstitution compared with GVHD mice in terms of cell numbers, activation phenotype, and cytokine production. We further demonstrated a preserved in vivo immune function using vaccinia infection and third-party skin-graft rejection models, suggesting that rsTreg immunosuppression was relatively specific of GVHD. Finally, we showed that rsTreg extensively proliferated during the first 2 weeks and then declined. In turn, donor Treg proliferated from day 15 on. Taken together, these results suggest that rsTreg GVHD prevention is associated with improved early immune reconstitution in a model that more closely approximates the biology of allogeneic HSCT in human adults.

Human effector CD8+ T cells derived from naive rather than memory subsets possess superior traits for adoptive immunotherapy

Cluster of differentiation (CD)8(+) T cells exist as naive, central memory, and effector memory subsets, and any of these populations can be genetically engineered into tumor-reactive effector cells for adoptive immunotherapy. However, the optimal subset from which to derive effector CD8(+) T cells for patient treatments is controversial and understudied. We investigated human CD8(+) T cells and found that naive cells were not only the most abundant subset but also the population most capable of in vitro expansion and T-cell receptor transgene expression. Despite increased expansion, naive-derived cells displayed minimal effector differentiation, a quality associated with greater efficacy after cell infusion. Similarly, the markers of terminal differentiation, killer cell lectin-like receptor G1 and CD57, were expressed at lower levels in cells of naive origin. Finally, naive-derived effector cells expressed higher CD27 and retained longer telomeres, characteristics that suggest greater proliferative potential and that have been linked to greater efficacy in clinical trials. Thus, these data suggest that naive cells resist terminal differentiation, or "exhaustion," maintain high replicative potential, and therefore may be the superior subset for use in adoptive immunotherapy.

Reversal of age-related thymic involution by an LHRH agonist in miniature swine

BACKGROUND AND AIMS OF STUDY: We have previously demonstrated a requirement for the presence of a juvenile thymus for the induction of transplantation tolerance to renal allografts by a short-course of calcineurin inhibition in miniature swine. We have also shown that aged, involuted thymi can be rejuvenated when transplanted as vascularized thymic lobes into juvenile swine recipients. The present studies were aimed at elucidating the extrinsic factors facilitating this restoration of function in the aged thymus. In particular, we tested the impact of sex steroid blockade by Luteinizing Hormone-Releasing Hormone (LHRH).

MATERIALS AND METHODS

30 naive animals (25 males and 5 females) were used for measurement of serum testosterone levels. 3 mature male pigs (aged at 22, 22 and 29 months old) were used to test the effects of Lupron (LHRH analog) injection at 45 mg (per 70-80 kg body weight) as a 3-month depot on testosterone levels and thymic rejuvenation. Thymic rejuvenation was assessed by histology, flow cytometric analysis, morphometric analysis and TREC assays.

RESULTS

Hormonal alterations were induced by Lupron and resulted in macroscopic and histologic regeneration of the thymus of aged animals within 2 months, as evidenced by restoration of juvenile thymus architecture and increased cellularity. Two animals that were evaluated for TREC both showed increased levels in the periphery following Lupron treatment.

CONCLUSION

Treatment of aged animals with Lupron leads to thymic rejuventaion in adult miniature swine. This result could expand the applicability of thymus-dependent tolerance-inducing regimens to adult recipients.

Impact of viable CD45 cells infused on lymphocyte subset recovery after unrelated cord blood transplantation in children

We studied lymphocyte recovery in 88 children who consecutively underwent unrelated cord blood transplantation for malignant (n = 64) or nonmalignant (n = 24) diseases. All children but 3 received myeloablative conditioning regimens with pretransplant antithymocyte globulin. Median age was 5.6 years (0.1-18 years) and median follow-up was 40 months (10-136 months). The median dose of infused viable CD45(+) cells (vCD45) was 3.35 × 10(7)/kg with a ratio infused vCD45/collected total nucleated cell at 0.46. Immunologic endpoints were: time to achieve CD3(+) >500 and 1500/mm(3), CD4(+) >500/mm(3), CD8(+) >250/mm(3), CD19(+) >200/mm(3), natural killer >100/mm(3). These endpoints were analyzed through the use of cumulative curves for estimating incidence over time in the context of competing risks, and through Fine and Gray models to assess prognostic factors. The median time to reach these endpoints was 33, 97, 214, and 340 days for natural killer, B, CD8, and CD4 cells, respectively. In multivariate analysis, a high infused vCD45 cell dose improved CD3 (P = .014) and CD4 (P = .032) reconstitutions. A young recipient age also favored CD3 recovery (P = .013). With patients grouped according to vCD45 cell dose quartiles, the threshold for a better recovery was 3.35 × 10(7)/kg. Considering the ratio vCD45/TNC, this "immune recovery based" threshold corresponds to a higher cell dose than the minimum usually recommended dose for myelogenous engraftment. This may have important implication for UCB selection.

HIV infection in the elderly

The prevalence of HIV in patients over the age of 50 years is increasing. Although older patients may achieve equal or better virologic suppression at equal rates compared with younger patients, the immunologic benefit of highly active antiretroviral therapy (HAART) in older patients may be reduced compared with younger patients. Comorbidities are more common in older patients than younger patients and can impact management of HIV in these patients. Providers must be cognizant of drug-drug interactions and side effects of HAART regimens when selecting an antiretroviral regimen in older HIV patients. As the HIV-infected population ages, there is a growing need to better determine the ideal HAART regimen and timing of HAART initiation in older patients.

Sex steroid ablation enhances immune reconstitution following cytotoxic antineoplastic therapy in young mice

Cytotoxic antineoplastic therapy is used to treat malignant disease but results in long-term immunosuppression in postpubertal and adult individuals, leading to increased incidence and severity of opportunistic infections. We have previously shown that sex steroid ablation (SSA) reverses immunodeficiencies associated with age and hematopoietic stem cell transplantation in both autologous and allogeneic settings. In this study, we have assessed the effects of SSA by surgical castration on T cell recovery of young male mice following cyclophosphamide treatment as a model for the impact of chemotherapy. SSA increased thymic cellularity, involving all of the thymocyte subsets and early T lineage progenitors. It also induced early repair of damage to the thymic stromal microenvironment, which is crucial to the recovery of a fully functional T cell-based immune system. These functional changes in thymic stromal subsets included enhanced production of growth factors and chemokines important for thymopoiesis, which preceded increases in both thymocyte and stromal cellularity. These effects collectively translated to an increase in peripheral and splenic naive T cells. In conclusion, SSA enhances T cell recovery following cyclophosphamide treatment of mice, at the level of the thymocytes and their stromal niches. This provides a new approach to immune reconstitution following antineoplastic therapy.

Alterations of the systemic environment are the primary cause of impaired B and T lymphopoiesis in telomere-dysfunctional mice

There is growing evidence that telomere dysfunction can contribute to human aging. Telomere dysfunction limits lymphopoiesis in aging telomerase knockout (mTerc(-/-)) mice primarily by the induction of stem cell-extrinsic alterations. The relative contribution of alterations in the stem cell niche and the systemic environment to the impairment of lymphopoiesis in response to telomere dysfunction is currently unknown. This study reveals a minor impact of stem cell-intrinsic defects on the impairment of B and T lymphopoiesis in response to telomere dysfunction. The impairment in B and T lymphopoiesis in aging telomere-dysfunctional mice was mainly due to alterations of the systemic environment. Telomere dysfunction had no significant cell-autonomous effects impairing the function of thymic or bone marrow niches in supporting B and T lymphopoiesis. Moreover, age-related alterations in the cellular composition of the thymic epithelium in telomere-dysfunctional mice were rescued by transplantation of the thymus into a wild-type environment; these rejuvenated thymi supported normal T lymphopoiesis in recipient mice. Together, these data place alterations in the systemic environment on top of the hierarchy of events limiting lymphopoiesis in response to telomere dysfunction.

Magnetic resonance imaging of radiation-induced thymic atrophy as a model for pathologic changes in acute feline immunodeficiency virus infection

The development of a protocol to reproducibly induce thymic atrophy, as occurs in feline immunodeficiency virus (FIV) infection and other immunosuppressive diseases, and to consistently estimate thymic volume, provides a valuable tool in the search of innovative and novel therapeutic strategies. Magnetic resonance imaging (MRI) using the short tau inversion recovery (STIR) technique, with fat suppression properties, was determined to provide an optimized means of locating, defining, and quantitatively estimating thymus volume in young cats. Thymic atrophy was induced in four, 8-10-week-old kittens with a single, directed 500 cGy dose of 6 MV X-rays from a clinical linear accelerator, and sequential MR images of the cranial mediastinum were collected at 2, 7, 14, and 21 days post irradiation (PI). Irradiation induced a severe reduction in thymic volume, which was decreased, on average, to 47% that of normal, by 7 days PI. Histopathology confirmed marked, diffuse thymic atrophy, characterized by reduced thymic volume, decreased overall cellularity, increased apoptosis, histiocytosis, and reduced distinction of the corticomedullary junction, comparable to that seen in acute FIV infection. Beginning on day 7 PI, thymic volumes rebounded slightly and continued to increase over the following 14 days, regaining 3-35% of original volume. These findings demonstrate the feasibility and advantages of using this non-invasive, in vivo imaging technique to measure and evaluate changes in thymic volume in physiologic and experimental situations. All experimental protocols in this study were approved by the Institutional Animal Care and Use Committee (IACUC) at Auburn University.

Cellular tumor vaccines administered after T cell-depleted allogeneic bone marrow transplantation induce effective anti-tumor immune responses

In allogeneic hematopoietic stem cell (HSC) transplantation, graft vs. tumor (GVT) activity contributes to the cancer cure. It is closely associated with graft vs. host disease (GVHD), an immune response initiated by transplanted donor T-cell responses against host minor histocompatibility antigens (mHAgs). GVHD is prevented by T-cell depletion of the donor graft, but T-cell depletion also abrogates curative GVT. We wished to test the hypothesis that cellular tumor vaccines administered after T cell-depleted HSC transplant can induce significant GVT effects, despite the absence of transplanted mature donor T cells. In this investigation, a murine model of major histocompatibility complex (MHC)-matched, mHAg-mismatched allogeneic HSC transplant was studied. T cell-depleted or normal T cell-containing grafts were given to myeloablated recipients. Following reconstitution the recipients were vaccinated with tumor vaccines. GVT responses were measured in vitro by T-cell function assays and flow cytometry, and in vivo by tumor burden or survival. Post-transplant tumor vaccines induced effective anti-tumor responses in recipients of T cell-depleted transplants, producing cytolytic and cytokine responses, reduced tumor burden and prolonged survival. Recipients of T cell-depleted transplants that still have significant thymic function may be suitable subjects for post-transplant vaccine therapy.