Antigen and Lymphopenia-Driven Donor T Cells Are Differentially Diminished by Post-Transplantation Administration of Cyclophosphamide after Hematopoietic Cell Transplantation

Abstract

Administration of cyclophosphamide following transplant (Post-transplant cyclophosphamide, PTC) has shown promise in the clinic as a prophylactic agent against graft vs. host disease. An important issue with regard to recipient immune function and reconstitution after PTC is the extent to which in addition to diminution of anti-host allo-reactive donor T cells, the remainder of the non-host allo-reactive donor T cell pool may be impacted. To investigate PTC’s effects on non-host reactive donor CD8 T cells, ova specific (OT-I) and gp100 specific Pmel-1 T cells were labeled with proliferation dyes and transplanted into syngeneic and allogeneic recipients. Notably, an intermediate dose (66mg/kg) of PTC which abrogated GVHD following allogeneic HSCT, did not significantly diminish these peptide specific donor T cell populations. Analysis of the rate of proliferation following transplant illustrated that lymphopenic driven donor non host reactive TCR Tg T cells in syngeneic recipients underwent slow division resulting in significant sparing of these donor populations. In contrast, following exposure to specific antigen at the time of transplant, these same T cells were significantly depleted by PTC demonstrating the global susceptibility of rapidly dividing T cells following encounter with cognate antigen. In total, our results employing both syngeneic and allogeneic minor antigen mismatched T cell replete models of transplantation, demonstrate a concentration of PTC that abrogates GVHD can preserve most cells that are dividing due to the accompanying lymphopenia following exposure. These findings have important implications with regard to immune function and reconstitution in recipients following allogeneic hematopoietic stem cell transplant.

Erratum: Modern approaches to HLA-haploidentical blood or marrow transplantation.

“…NRM was 15% after 1 year of follow-up. 124 Consistent with preclinical data suggesting sparing of non-alloreactive T cells, 115,125 no patients had cytomegalovirus disease; only two died from fungal infections (one had graft failure). 124 Longer follow up of expanded cohorts treated in line with the JHH protocol confirmed low rates of NRM, acute GVHD and chronic GVHD.…”

“…111,114 Parallel to the effects seen on host T cells in skin allograft models, in mouse alloBMT models, the tolerogenic effects of PTCy were exerted through elimination of alloreactive donor T cells. 115 Donor T cells exposed to host antigens on day 0 were largely depleted, whereas non-alloreactive donor T cells, which divided more slowly in a lymphopenic environment, were relatively spared. 115 However, destruction of alloreactive donor T cells was necessary but not sufficient for PTCy-induced tolerance: in mouse models of MHCmatched alloBMT in which donor CD4 + T cells promote GVHD, as well as in xenograft models, donor T REG cells were necessary to prevent lethal GVHD after PTCy treatment, 116,117 an effect consistent with the results from skin allograft models.…”

“…115 Donor T cells exposed to host antigens on day 0 were largely depleted, whereas non-alloreactive donor T cells, which divided more slowly in a lymphopenic environment, were relatively spared. 115 However, destruction of alloreactive donor T cells was necessary but not sufficient for PTCy-induced tolerance: in mouse models of MHCmatched alloBMT in which donor CD4 + T cells promote GVHD, as well as in xenograft models, donor T REG cells were necessary to prevent lethal GVHD after PTCy treatment, 116,117 an effect consistent with the results from skin allograft models. Donor T REG cells in both mouse and human models of alloBMT were resistant to PTCy-induced cytotoxicity owing to increased expression of aldehyde dehydrogenase, the enzyme primarily responsible for in vivo detoxification of cyclophosphamide, 118 upon alogeneic stimulation in a lymphopenic environment.…”

“…115,122 Coupled with the finding that high-dose cyclophosphamide was not toxic to haematopoietic stem cells owing to their high aldehyde dehydrogenase expression, and supportive clinical studies showing that high-dose cyclophosphamide could be safely administered to patients with autoimmunity without requiring stem-cell rescue, 118 the use of high-dose PTCy for GVHD prophylaxis was explored clinically. In a phase I study of 13 patients at the Johns Hopkins Hospital (JHH), the findings of which were published in 2002, patients received 50 mg/kg PTCy 3 days after receiving TCR-haploBMT using RIC with fludarabine, cyclophosphamide (cohort 2 only) and low-dose (200 cGy) TBI.…”

T-cell replete haploidentical donor transplantation using post-transplant CY: an emerging standard-of-care option for patients who lack an HLA-identical sibling donor

“…More recent investigations have demonstrated that alloreactive T cells proliferating in response to antigen (that is, those responsible for GVHD and graft rejection) are much more susceptible to the effects of ptCY than memory T cells (such as those responsible for immunity to pathogens post transplant) which proliferate more slowly in response to lymphopenia. 16 Furthermore, CD4(+)CD45RA(− )Foxp3 (+hi) effector regulatory T cells express high levels of aldehyde dehydrogenase and appear to readily survive the use of high-dose CY and may contribute to the prevention of GVHD following Haplo-post-HCT-CY. 17 Based upon some of these observations, the group at Johns Hopkins University translated this approach into a clinical protocol of HaploD transplantation using a non-myeloablative conditioning regimen (pre-transplant fludarabine (150 mg/m 2 ), CY (29 mg/kg) and 2 Gy TBI, a T-replete BM graft followed by ptCY (50 mg/kg on d+3), MMF (day 4 to 35) and tacrolimus (day 4 to >50).…”