Adoptive Cellular Therapy for Cytomegalovirus Following Allogeneic Stem Cell Transplantation: Toxicity and Efficacy.

Adoptive transfer of virus-specific T-cells offers the potential for accelerating reconstitution of antigen-specific immunity and limiting the morbidity and mortality of viral infections following allogeneic stem cell transplantation. However, the logistics of producing virus-specific T-cells and the risk of inducing GvHD secondary to the infusion of alloreactive clones has limited the application of cellular therapies (CT). We have treated 37 allogeneic transplant recipients on 2 consecutive CT studies with CMV-specific T-cell lines generated by short-term ex-vivo culture of donor lymphocytes with donor monocyte-derived dendritic cells pulsed with virus-lysate. Culture resulted in generation of both CD4+ and CD8+ CMV-specific T cells as demonstrated by antigen-specific γ-interferon production (1.2–4.8% of CD4+ cells, 0.2–6.5% of CD8+ cells) and HLA-tetramer binding. These cells were capable of HLA-restricted CMV-specific target lysis. Thirty-one patients were treated on a pre-emptive protocol based on PCR surveillance, expanded to include those with multiple reactivations/disease. Total cultured cell dose infused was 1 x 10⁵/kg, returned at a median of 39 (range 4–410) days post-transplant. Six have been entered on a subsequent prophylactic study, receiving the same dose at day 28 post-transplant. Five of these had CMV DNA detectable by PCR at the time of CT. The preparative regimen included T-cell depletion (alemtuzumab) in thirty-one. Ten had unrelated donors (5 mismatched at one and 1 at two HLA loci). Thirty-four recipients were CMV seropositive. Thirty-two were receiving cyclosporine at the time of infusion. One was also receiving mycophenolate, and one both mycophenolate and steroids for hemolysis. Eleven had prior GvHD (5 Grade I, 5 Grade II, 1 extensive chronic). Twenty-eight were treated during their first episode of post-transplant CMV infection, five during the second, two the third and one the seventh. Two had active CMV disease (biopsy proven CMV colitis) and six were receiving anti-viral drug therapy at the time of infusion. Fifteen patients required no antiviral therapy. In 16/30 cases given ACT at a time when CMV DNA was detectable antiviral therapy was given for subsequently increasing viral titre. Both cases of CMV disease resolved and there were no additional cases following CT. Following viral clearance there were only 4 episodes of subsequent CMV infection requiring therapy in 32 evaluable cases (including 1 treated prophylactically) compared to 45/72 historical controls (p<0.0001) Two occurred following increased immune suppression (including steroids) for ongoing or newly developed immune-mediated hemolysis. GvHD occurred in 12/32 evaluable patients following ACT (4 Grade I, 1 Grade III acute GvHD, 3 limited and 4 extensive chronic GvHD). Six cases were in unrelated donor or T-replete transplants, and six were in patients with a prior history of GvHD. Massive expansions of mainly CD8+ T-cells developed in concert with resolving viremia. Infused CMV-specific clones were demonstrated to expand (contributing up to 35% of the CD8+ population) and persist for at least 6 months following infusion. In conclusion, our updated experience demonstrates that cellular therapy for CMV is both feasible and effective in a clinical environment, and that it can be delivered with minimal toxicity allowing consideration of expanded prophylactic application.