TCRα/ß Depleted Mobilized Pbscs without Calcineurin Inhibitors in Patients with Fanconi Anemia

Background

We performed a single center phase II prospective clinical trial (NCT03579875) to test the hypothesis that TCRα/ß depletion would sufficiently deplete GVHD causing α/ß T cells to eliminate the need for prolonged immunosuppression after PBSC transplantation in patients with FA.

Methods

Patients received conditioning regimen (MacMillan, Blood 2015) with fludarabine, cyclophosphamide and methylprednisolone alone if the patient had marrow failure only and an HLA matched sibling donor (n=2), or with total body irradiation with thymic shielding (n=12) or busulfan (n=17) if there was clonal disease, or if a haploidentical related or HLA matched or mismatched unrelated donor. All but the first patient received one dose of rituximab on day-1 for B cell depletion. Mycophenolate mofetil was given after transplant if the TCRα/ß dose ≥2 × 10⁵ TCR α/β T cells/kg recipient (n=4). Mass cytometry (CyTOF) studies included targeting markers for delineating naïve, effector and effector memory CD4 cells and naïve, stem memory, central memory and effector memory CD8 cells, as well as T regulatory, B and γδ T cell subpopulations.

Results

31 patients with FA, median 9.5 years (range 1.7-43.8) were enrolled. Patients had marrow failure (n=18), MDS (n=4), relapsed MDS (n=1), APML (n=1), ALL (n=1), immune deficiency (n=1), BRCA2 with clonal abnormality (n=2) or pre-emptively for BRCA2 (n=3), with 2 patients having had a prior transplant. Neutrophil engraftment occurred in all patients, median 9 days (Figure A). Platelet recovery occurred in 30 patients, median 15 days. To date, 3 patients developed grade II-IV acute GVHD. No patient has developed chronic GVHD requiring systemic therapy (Figure B). Probability of survival at 2 years is 90%, including 5/6 BRCA2 patients and all 7 adult patients (Figure C).

By 1 year, only 6 patients developed viral infections requiring systemic therapy. Immune recovery in 15 patients was compared to 10 historical FA patients similarly transplanted except for GVHD prophylaxis (TCD by CD34+ selection with calcineurin inhibitor, CNI). Significant finding were: lower proportions of total CD4+ cells (43.0% vs 76.7%, p <0.0002), and memory Tregs (4.8% vs 14.6%, p<0.01), and higher proportions of γδ T cells (30.8% vs 4.8%, p<0.0003) in recipients of TCRα/ß PBSC at day 28. Analysis of γδ T cell proportions at 6 months (16.2% vs 3.2%, p=0.0106; TCRa/bPBSC vs. CD34 selection) indicated that TCRα/ß depletion resulted in a lasting immune imprint, underpinning the differences in reconstitution between these two transplant methodologies (Figure D).

Conclusions

TCRα/ß depleted PBSC transplantation without CNI results in excellent engraftment, minimal GVHD, few viral infections and excellent survival in FA patients with promising outcomes in those with hematologic malignancy, biallelic BRCA2 genotype and older age who historically often did poorly.