Sirolimus, Post–Transplant Cyclophosphamide, and CTLA4-Ig Maintain Stable Mixed Chimerism In a Mismatched Murine Model

Hematopoietic stem cell transplantation (HSCT) is the only curative option for patients with sickle cell disease (SCD). We sought to extend our haploidentical HSCT regimen with nonmyeloablative conditioning. The objective of our study was to assess the ability of the immunosuppressive agent CTLA4-Ig to induce mixed chimerism in the haploidentical HSCT setting when combined with sirolimus, post-transplant cyclophosphamide (PT-Cy), or both.

We used a mismatched mouse model with BALB/c donors and C57BL/6 recipients. Recipient mice received 200 cGy TBI on day of the transplant and were conditioned with or without sirolimus, PT-Cy, and/or CTLA4-Ig.

Our data show that when CTLA4-Ig alone or CTLA4-Ig/PT-Cy are given, donor cells are not detected. However, mixed chimerism is maintained in mice who received either sirolimus/PT-Cy or sirolimus/PT-Cy given together with CTLA4-Ig over 60 days. Additionally our data indicate a significant increase in recovery of donor cells within CD8 T-cell, CD19 B-cell, and CD11b myeloid cell populations in groups conditioned with sirolimus/PT-Cy, or sirolimus/PT-Cy/CTLA4-Ig as compared to groups conditioned with CTLA4-Ig (p=0.003; p=0.002; p=0.049) alone or CTLA4-Ig/PT-Cy (p=0.001; p<0.0001; p=0.001) at 30 days, respectively.

These data demonstrate that sirolimus in combination with PT-Cy and CTLA4-Ig is synergistic in an MHC-mismatched mouse model. The novel tri-drug group establishes mixed chimerism while conditioning with CTLA4-Ig alone or CTLA4-Ig/PT-Cy does not. The data also identify induction of stable mixed chimerism in specific cellular subpopulations within the sirolimus/PT-Cy and sirolimus/PT-Cy/CTLA4-Ig groups, indicating that these cells may play an important role in HCST.

Addition of rapamycin to anti-CD3 antibody improves long-term glycaemia control in diabetic NOD mice

Aims/Hypothesis

Non-Fc-binding Anti CD3 antibody has proven successful in reverting diabetes in the non-obese diabetes mouse model of type 1 diabetes and limited efficacy has been observed in human clinical trials. We hypothesized that addition of rapamycin, an mTOR inhibitor capable of inducing operational tolerance in allogeneic bone marrow transplantation, would result in improved diabetes reversal rates and overall glycemia.

Methods

Seventy hyperglycemic non-obese diabetic mice were randomized to either a single injection of anti CD3 alone or a single injection of anti CD3 followed by 14 days of intra-peritoneal rapamycin. Mice were monitored for hyperglycemia and metabolic control.

Results

Mice treated with the combination of anti CD3 and rapamycin had similar rates of diabetes reversal compared to anti CD3 alone (25/35 vs. 22/35). Mice treated with anti CD3 plus rapamycin had a significant improvement in glycemia control as exhibited by lower blood glucose levels in response to an intra-peritoneal glucose challenge; average peak blood glucose levels 30 min post intra-peritoneal injection of 2 gr/kg glucose were 6.9 mmol/L in the anti CD3 plus rapamycin group vs. 10 mmo/L in the anti CD3 alone (P<0.05).

Conclusions/Interpretation

The addition of rapamycin to anti CD3 results in significant improvement in glycaemia control in diabetic NOD mice.

Nonmyeloablative conditioning employing busulfan and sirolimus permits donor-dominant stable chimerism in a murine model of haploidentical allogeneic stem cell transplantation (P2192)

Allogeneic stem cell transplant (SCT) is a potentially curative option for many hematologic diseases, yet donor availability remains a challenge, and haploidentical SCT is associated with a higher risk of rejection. We successfully translated a model based on total-body irradiation (TBI) with to humans; however, TBI involves toxicities and risk of malignant side-effects, and we hypothesize that busulfan may be a superior alternative in some settings. G-CSF-mobilized F1/J (C57BL/6-BALB/c hybrid) splenocytes were injected into C57BL/6 hosts who had received 10-30mg/kg IP busulfan the previous day. All recipients received 31 days of 3mg/kg IP sirolimus beginning the day before transplant. No GvHD was observed and counts recovered by week 8 in all groups. Mice conditioned with 30mg/kg busulfan displayed remarkably high donor chimerism (&gt;90%), which was significantly higher than 300cGy TBI-conditioned control mice (64-86%) across all timepoints. Mice receiving 30mg/kg or 20mg/kg busulfan maintained stable chimerism for over 18 months. Mice conditioned with 10mg/kg busulfan showed only transient chimerism through 4 weeks. Proliferation of CD4+ cells in response to donor increases with decreasing busulfan, and mice receiving 30mg/kg responded more strongly than mice receiving TBI. A memory effect was observed in mice that received 10mg/kg busulfan and lost their grafts. Notably, a slightly higher incidence of host-derived Tregs in mice was also observed after graft rejection.

High-efficiency transduction of rhesus hematopoietic repopulating cells by a modified HIV1-based lentiviral vector

Human immunodeficiency virus type 1 (HIV1) vectors poorly transduce rhesus hematopoietic cells due to species-specific restriction factors, including the tripartite motif-containing 5 isoformα (TRIM5α) which targets the HIV1 capsid. We previously developed a chimeric HIV1 (χHIV) vector system wherein the vector genome is packaged with the simian immunodeficiency virus (SIV) capsid for efficient transduction of both rhesus and human CD34(+) cells. To evaluate whether χHIV vectors could efficiently transduce rhesus hematopoietic repopulating cells, we performed a competitive repopulation assay in rhesus macaques, in which half of the CD34(+) cells were transduced with standard SIV vectors and the other half with χHIV vectors. As compared with SIV vectors, χHIV vectors achieved higher vector integration, and the transgene expression rates were two- to threefold higher in granulocytes and red blood cells and equivalent in lymphocytes and platelets for 2 years. A recipient of χHIV vector-only transduced cells reached up to 40% of transgene expression rates in granulocytes and lymphocytes and 20% in red blood cells. Similar to HIV1 and SIV vectors, χHIV vector frequently integrated into gene regions, especially into introns. In summary, our χHIV vector demonstrated efficient transduction for rhesus long-term repopulating cells, comparable with SIV vectors. This χHIV vector should allow preclinical testing of HIV1-based therapeutic vectors in large animal models.

The assessment of human erythroid output in NOD/SCID mice reconstituted with human hematopoietic stem cells

The third-generation NOD/LtSz-scid/IL2Rγ(null) (NOD/SCID IL2Rγ(null)) mouse represents a significantly improved xenograft model allowing high levels of human leukocyte engraftment over extended follow up. One remaining limitation of this mouse model, however, is the low level of circulating human erythrocytes. We established a practical ex vivo erythroid culture system of xenograft marrow progenitors to enrich for human erythroid progeny. At various time points after transplant, erythroid cells were easily assayed after 17 days of ex vivo culture of xenograft marrow, with nearly all nucleated cells of human origin and approximately 60% human GPA or CD71 positive. We then transplanted cord blood CD34(+) cells marked with a lentiviral vector encoding green fluorescent protein (GFP). Three months later, ex vivo culture of xenograft marrow progenitors showed 41.3% of the cultured erythroid cells were positive for GFP and human CD71, and 56.2% were positive for GFP and human GPA, similar to that of circulating leukocytes at the same time point. Next, G-CSF mobilized peripheral blood CD34(+) cells from a sickle cell trait subject were infused in this mouse model to determine if the hemoglobin pattern could be modeled. CD34(+) cells from the sickle cell trait subject engrafted equally compared to CD34(+) cells from normal subjects, establishing the sickle cell trait phenotype. Lastly, a comparison of adult-derived peripheral blood CD34(+) cells and cord blood-derived CD34(+) cells xenografted mice was made, and long term follow-up demonstrated a recapitulation of the fetal to adult hemoglobin switch. This approach should prove a useful tool for testing strategies for genetic manipulation of erythroid progeny and the study of hemoglobin switching.

Transient in vivo beta-globin production after lentiviral gene transfer to hematopoietic stem cells in the nonhuman primate

Inherited disorders of globin synthesis remain desirable targets for hematopoietic stem cell (HSC)-based therapies. Gene transfer using retroviral vectors offers an alternative to allogeneic HSC transplantation by the permanent integration of potentially therapeutic genes into primary autologous HSCs. Although proof of principle has been demonstrated in humans, this approach has been met by formidable obstacles, and large-animal models have become increasingly important for the preclinical development of gene addition strategies. Here we report lentiviral gene transfer of the human beta-globin gene under the control of the globin promoter and large fragments of the globin locus control region (LCR) in the nonhuman primate. Using an HIV-1, vesicular stomatitis virus glycoprotein G (VSV-G)-pseudotyped vector, modified to overcome a species-specific restriction to HIV-1, gene transfer to colony-forming units (CFU) derived from mobilized peripheral blood (PB) rhesus CD34+ cells was 84.4 +/- 2.33%. Erythroid cells derived from transduced rhesus CD34+ cells expressed human beta-globin at high levels as assessed by flow cytometry with a human beta-globin-specific antibody. Two rhesus macaques (RQ3586 and RQ3583) were transplanted with mobilized PB CD34+ cells transduced with our modified HIV vector at a multiplicity of infection of 80. High gene transfer rates to CFUs were achieved in vitro (RQ3586, 87.5%; RQ3583, 83.3%), with efficient human beta-globin expression among erythroid progeny generated in vitro. Early posttransplantation, gene transfer rates of 5% or higher were detectable and confirmed by genomic Southern blotting, with equivalent-level human beta-globin expression detected by flow cytometry. Long-term gene marking levels among mononuclear cells and granulocytes assessed by quantitative polymerase chain reaction gradually decreased to about 0.001% at 2 years, likely due to additional HIV-1 restrictive elements in the rhesus macaque. No evidence of clonal hematopoiesis has occurred in our animals in up to 2 years. Current efforts are aimed at developing a lentiviral vector capable of efficiently transducing both human and rhesus HSCs to allow preclinical modeling of globin gene transfer.

Busulfan produces efficient human cell engraftment in NOD/LtSz-Scid IL2Rgamma(null) mice

Xenografting immunodeficient mice after low-dose irradiation has been used as a surrogate human hematopoietic stem cell (HSC) assay; however, irradiation requires strict and meticulous animal support and can produce significant mortality rates, limiting the usefulness of this model. In this work, we examined the use of parenteral busulfan as an alternative conditioning agent. Busulfan led to dose-dependent human HSC engraftment in NOD/LtSz-scid/IL2Rgamma(null) mice, with marked improvement in survival rates. Terminally differentiated B and T lymphocytes made up most of the human CD45+ cells observed during the initial 5 weeks post-transplant when unselected cord blood (CB) products were infused, suggesting derivation from existing mature elements rather than HSCs. Beyond 5 weeks, CD34+-enriched products produced and sustained superior engraftment rates compared with unselected grafts (CB CD34+, 65.8% +/- 5.35%, vs. whole CB, 4.27% +/- 0.67%, at 24 weeks). CB CD34+ group achieved significantly higher levels of engraftment than mobilized CD34+-enriched peripheral blood (PB CD34+). At 8 weeks, all leukocyte subsets were detected, yet human red blood cells (RBCs) were not observed. Transfused human red cells persisted in the chimeric mice for up to 3 days; an accompanying rise in total bilirubin suggested hemolysis as a contributing factor to their clearance. Recipient mouse-derived human HSCs had the capacity to form erythroid colonies in vitro at various time points post-transplant in the presence of human transferrin (Tf). When human Tf was administered singly or in combination with anti-CD122 antibody and human cytokines, up to 0.1% human RBCs were detectable in the peripheral blood. This long evasive model should prove valuable for the study of human erythroid cells.

Long-term vector integration site analysis following retroviral mediated gene transfer to hematopoietic stem cells for the treatment of HIV infection

We previously reported the efficacy of nonmyeloablative allogeneic transplantation in 2 HIV positive recipients, one of whom received retrovirus transduced hematopoietic stem cells to confer resistance to HIV. Here we report an assessment of retroviral integration sites (RISs) recovered out to 3 years post-transplantation. We identified 213 unique RISs from the patient's peripheral blood samples by linear amplification-mediated PCR (LAM-PCR). While vector integration patterns were similar to that previously reported, only 3.76% of RISs were common among early (up to 3 months) and late samples (beyond 1 year). Additionally, common integration sites were enriched among late samples (14.9% vs. 36.8%, respectively). Three RISs were found near or within known oncogenes, but 2 were limited to early timepoints. Interestingly, an integration site near the MDS1 gene was detected in long-term follow-up samples; however, the overall contribution of MDS1 integrated clone remained stably low during follow-up.