Regulatory T-cell depletion does not prevent emergence of new CD25+ FOXP3+ lymphocytes after antigen stimulation in culture

Isolation of highly suppressive CD25+FoxP3+ T regulatory cells from G-CSF-mobilized donors with retention of cytotoxic anti-viral CTLs: application for multi-functional immunotherapy post stem cell transplantation

Previous studies have demonstrated the effective control of cytomegalovirus (CMV) infections post haematopoietic stem cell transplant through the adoptive transfer of donor derived CMV-specific T cells (CMV-T). Strategies for manufacturing CMV immunotherapies has involved a second leukapheresis or blood draw from the donor, which in the unrelated donor setting is not always possible. We have investigated the feasibility of using an aliquot of the original G-CSF-mobilized graft as a starting material for manufacture of CMV-T and examined the activation marker CD25 as a targeted approach for identification and isolation following CMVpp65 peptide stimulation. CD25+ cells isolated from G-CSF-mobilized apheresis revealed a significant increase in the proportion of FoxP3 expression when compared with conventional non-mobilized CD25+ cells and showed a superior suppressive capacity in a T cell proliferation assay, demonstrating the emergence of a population of Tregs not present in non-mobilized apheresis collections. The expansion of CD25+ CMV-T in short-term culture resulted in a mixed population of CD4+ and CD8+ T cells with CMV-specificity that secreted cytotoxic effector molecules and lysed CMVpp65 peptide-loaded phytohaemagglutinin-stimulated blasts. Furthermore CD25 expanded cells retained their suppressive capacity but did not maintain FoxP3 expression or secrete IL-10. In summary our data indicates that CD25 enrichment post CMV stimulation in G-CSF-mobilized PBMCs results in the simultaneous generation of both a functional population of anti-viral T cells and Tregs thus illustrating a potential single therapeutic strategy for the treatment of both GvHD and CMV reactivation following allogeneic haematopoietic stem cell transplantation. The use of G-CSF-mobilized cells as a starting material for cell therapy manufacture represents a feasible approach to alleviating the many problems incurred with successive donations and procurement of cells from unrelated donors. This approach may therefore simplify the clinical application of adoptive immunotherapy and broaden the approach for manufacturing multi-functional T cells.

Genetically engineered fixed K562 cells: potent "off-the-shelf" antigen-presenting cells for generating virus-specific T cells

BACKGROUND AIMS

The human leukemia cell line K562 represents an attractive platform for creating artificial antigen-presenting cells (aAPC). It is readily expandable, does not express human leukocyte antigen (HLA) class I and II and can be stably transduced with various genes.

METHODS

In order to generate cytomegalovirus (CMV) antigen-specific T cells for adoptive immunotherapy, we transduced K562 with HLA-A∗0201 in combination with co-stimulatory molecules.

RESULTS

In preliminary experiments, irradiated K562 expressing HLA-A∗0201 and 4-1BBL pulsed with CMV pp65 and IE-1 peptide libraries failed to elicit antigen-specific CD8⁺ T cells in HLA-A∗0201⁺ peripheral blood mononuclear cells (PBMC) or isolated T cells. Both wild-type K562 and aAPC strongly inhibited T cell proliferation to the bacterial superantigen staphylococcal enterotoxin B (SEB) and OKT3 and in mixed lymphocyte reaction (MLR). Transwell experiments suggested that suppression was mediated by a soluble factor; however, MLR inhibition was not reversed using transforming growth factor-β blocking antibody or prostaglandin E2 inhibitors. Full abrogation of the suppressive activity of K562 on MLR, SEB and OKT3 stimulation was only achieved by brief fixation with 0.1% formaldehyde. Fixed, pp65 and IE-1 peptide-loaded aAPC induced robust expansion of CMV-specific T cells.

CONCLUSIONS

Fixed gene-modified K562 can serve as effective aAPC to expand CMV-specific cytotoxic T lymphocytes for therapeutic use in patients after stem cell transplantation. Our findings have implications for broader understanding of the immune evasion mechanisms used by leukemia and other tumors.

Donor lymphocyte count and thymic activity predict lymphocyte recovery and outcomes after matched-sibling hematopoietic stem cell transplant

Delayed immune recovery is a characteristic feature of allogeneic hematopoietic stem cell transplantation in adult recipients. Although recipient thymic T-cell neogenesis contributes to T-cell regeneration after transplantation, thymic recovery in the transplant recipient decreases with increasing age, and is diminished by intensive preconditioning regimens and graft-versus-host disease. In adult recipients, most events that determine transplant success or failure occur during the period when the majority of circulating T cells is derived from the donor's post thymic T-cell repertoire. As a result, the make-up of the donor lymphocyte compartment may strongly influence immune recovery and transplant outcomes. The aim of this study was to examine donor lymphocyte counts in a series of patients undergoing an allogeneic hematopoietic stem cell transplant to identify the potential contribution of donor regulatory and conventional T lymphocyte populations to immune recovery and transplant outcomes. We examined donor lymphocyte subset counts in relation to post-transplant lymphocyte recovery and transplant events in 220 consecutive myeloablative, T-cell-depleted, HLA-identical sibling hematopoietic stem cell transplant recipients with hematologic malignancies. In a multivariate analysis, absolute numbers of donor CD4(+) recent thymic emigrants were associated with overall survival (P=0.032). The donors' absolute lymphocyte count and thymic production of regulatory T cells were both associated with extensive chronic graft-versus-host disease (P=0.002 and P=0.022, respectively). In conclusion, these results identify donor immune characteristics that are associated with lymphocyte recovery, extensive chronic graft-versus-host disease, and survival in the recipient following allogeneic hematopoietic stem cell transplantation. The study reported here was performed using peripheral blood samples drawn from donors and patients enrolled in the ClinicalTrials.gov-registered trials NCT00001623, NCT00001873, NCT00353860, NCT00066300, NCT00079391, and NCT00398346.

Evolution of the donor T-cell repertoire in recipients in the second decade after allogeneic stem cell transplantation

After allogeneic stem cell transplantation (SCT), T lymphocyte function is reestablished from the donor's postthymic T cells and through thymic T-cell neogenesis. The immune repertoire and its relation to that of the donor have not been characterized in detail in long-term adult SCT survivors. We studied 21 healthy patients in their second decade after a myeloablative SCT for hematologic malignancy (median follow-up, 12 years). Immune profiles were compared with donor samples cryopreserved at transplant and beyond 10 years from SCT. Only one recipient was on continuing immunosuppression. Compared with the donor at transplant, there was no significant difference in CD4, CD8, natural killer, and B-cell blood counts. However, compared with donors, recipients had significantly fewer naive T cells, lower T-cell receptor excision circle levels, fewer CD4 central memory cells, more effector CD8(+) cells, and more regulatory T cells. TCR repertoire analysis showed no significant difference in complexity of TCRVβ spectratype between recipients and donors, although spectratype profiles had diverged with both gain and loss of donor repertoire peaks in the recipient. In conclusion, long-term allogeneic SCT survivors have subtle defects in their immune profile consistent with defective thymic function but compatible with normal health. This study is registered at http://www.clinicaltrials.gov as NCT00106925.

Alloreactivity across HLA barriers is mediated by both naïve and antigen-experienced T cells

T cell responses to allogeneic targets arise predominantly from the naïve pool. However, in humans, the risk of graft-versus-host disease is increased if the donor has circulating T cells recognizing multiple persistent DNA viruses, suggesting that memory T cells also contribute to the alloresponse. To examine HLA alloreactivity, we used flow cytometry-based proliferation and cytokine production assays. We identified the clonal identity of virus-specific T cells cross-reacting with HLA-disparate targets by sequencing the T cell receptor β chains in virus-specific T cell lines restimulated with cognate and HLA-disparate targets and sorting these chains according to cytokine response. We confirmed that naïve T cells from cord blood and adult individuals responded to HLA-mismatched target cells. In addition, in adults, we identified memory T cells responding by cytokine release to HLA-mismatched targets both in direct assays and after 8 days of culture with allogeneic stimulator cells. Epstein-Barr virus-specific and cytomegalovirus-specific T cells, tested against a panel of 30 T cell antigen-presenting cells with a broad coverage of the most prominent HLA types, displayed specificity for certain mismatched HLA alleles. Sequencing of the T cell receptor β chain demonstrated a clonotypic identity of cells that responded to both viral and allogeneic stimulation. These findings show conclusively that alloresponses in humans are not confined to the naïve T cell subset, and that memory viral antigen-specific T cells can cross-react with specific mismatched HLA-peptide complexes not presenting with cytomegalovirus or Epstein-Barr virus peptides.

Allogeneic virus-specific T cells with HLA alloreactivity do not produce GVHD in human subjects

Adoptive transfer of viral antigen-specific memory T cells can reconstitute antiviral immunity, but in a recent report a majority of virus-specific cytotoxic T-lymphocyte (CTL) lines showed in vitro cross-reactivity against allo-human leukocyte antigen (HLA) molecules as measured by interferon-γ secretion. We therefore reviewed our clinical experience with adoptive transfer of allogeneic hematopoietic stem cell transplantation donor-derived virus-specific CTLs in 153 recipients, including 73 instances where there was an HLA mismatch. There was no de novo acute graft-versus-host disease after infusion, and incidence of graft-versus-host disease reactivation was low and not significantly different in recipients of matched or mismatched CTL. However, we found that virus-specific T cell lines recognized up to 10% of a panel of 44 HLA disparate targets, indicating that virus-specific T cells can have cross-reactivity with HLA-mismatched targets in vitro. These data indicate that the adoptive transfer of partially HLA-mismatched virus-specific CTL is safe despite in vitro recognition of recipient HLA molecules.

The transfer of adaptive immunity to CMV during hematopoietic stem cell transplantation is dependent on the specificity and phenotype of CMV-specific T cells in the donor

The successful reconstitution of adaptive immunity to human cytomegalovirus (CMV) in hematopoietic stem cell transplantation (HSCT) recipients is central to the reduction of viral reactivation-related morbidity and mortality. Here, we characterized the magnitude, specificity, phenotype, function, and clonotypic composition of CMV-specific T-cell responses in 18 donor-recipient pairs both before and after HSCT. The principal findings were: (1) the specificity of CMV-specific T-cell responses in the recipient after HSCT mirrors that in the donor; (2) the maintenance of these targeting patterns reflects the transfer of epitope-specific T-cell clonotypes from donor to recipient; (3) less differentiated CD27(+)CD57(-) CMV-specific memory T cells are more likely to persist in the recipient after HSCT compared with more terminally differentiated CD27(-) CD57(+) CMV-specific memory T cells; (4) the presence of greater numbers of less differentiated CD8(+) CMV-specific T cells in the donor appears to confer protection against viral reactivation in the recipient after HSCT; and (5) CMV-specific T cells acquire a more differentiated phenotype and a restricted functional profile after HSCT. Overall, these findings define the immunologic factors that influence the successful adoptive transfer of antigen-specific T-cell immunity during HSCT, which enables the identification of recipients at particular risk of CMV reactivation after HSCT.