Allogeneic hematopoietic cell transplantation (HCT) may be curative for patients with marrow and immune disorders, but graft-vs-host-disease (aGVHD) and infections cause significant morbidity and non-relapse mortality. We have conducted a multicenter, double blind, placebo-controlled phase II trial of costimulation blockade with abatacept (Aba) combined with standard GVHD prophylaxis with a calcineurin inhibitor and methotrexate (CNI + MTX) following HLA matched unrelated donor transplant (n=142).

In order to assess the effects of Aba on immune reconstitution, and to assess whether this reconstitution is influenced during CMV reactivation, we longitudinally evaluated post-transplant whole blood samples with multiparameter flow cytometry using markers for CD3, CD4, CD8, CD197 and CD45RA to measure reconstitution of CD4 and CD8 T cell populations and their respective memory subsets over time.

Results: We observe that post-transplant CMV reactivation induces a marked expansion of CD8 effector memory (EM) cells, which is similar in magnitude for Aba vs placebo patients. We found that development of moderate (gr 2-4) or severe (gr 3-4) GVHD was not associated with an increased frequency of CMV reactivation, but patients with moderate GVHD showed a blunted expansion of CD8 EM cells compared to those without GVHD, and CD8 EM expansion was essentially absent among CMV reactivating patients with severe aGVHD. Clinical correlates will be presented.

Conclusions: Our results suggest that adding abatacept to CNI/MTX does not materially affect reconstitution of T cell immunity in the presence or absence of CMV reactivation, but aGVHD remains a major driver of compromised immune recovery after HCT.

Disclosures

Watkins:Bristol Myers Squibb: Research Funding. Qayed:Mesoblast: Consultancy; Novartis: Consultancy. Horan:Bristol Myers Squib: Honoraria, Research Funding. Kean:gilead: Research Funding; bluebird bio: Research Funding; fortyseven: Consultancy; magenta: Research Funding; regeneron: Research Funding; hifibio: Consultancy; kymab: Consultancy; Bristol Meyers Squibb: Research Funding; novartis: Consultancy. Langston:Kadmon Corporation: Research Funding; Bristol Myers Squib: Research Funding; Incyte: Research Funding; Chimerix: Research Funding; Takeda: Research Funding; Astellas Pharmaceuticals: Research Funding; Jazz Pharmaceuticals: Research Funding.

Author notes

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Asterisk with author names denotes non-ASH members.