Cytomegalovirus (CMV) infection remains an important cause of morbidity and mortality in patients undergoing allogeneic stem cell transplantation (SCT). This is particularly true in patients transplanted using volunteer unrelated donors (VUDs) where despite improvements in antiviral therapy CMV positive serostatus remains an adverse prognostic indicator. Adoptive transfer of donor-derived CMV-specific CD8+ T cell clones reduces the rate of viral reactivation but the complexity of this approach severely limits its clinical application.

We have previously reported the purification of CMV-specific CD8+ cytotoxic T lymphocytes (CMV-CTL) from the blood of stem cell transplant donors using HLA-peptide tetramers and their subsequent transfer. Six patients undergoing stem cell transplantation from HLA identical sibling donors were studied. CMV-CTL were infused on a pre-emptive basis in patients who developed evidence of CMV viremia. All patients showed prompt and durable CMV-specific immune reconstitution demonstrating durable CMV-specific immune reconstitution. CMV-CTL constituted up to 21% of the patient lymphocyte CD8+ T cell compartment and were detectable up to 24 months in all patients. There was a reduced requirement for anti-viral agents in treated patients (33%) compared with a control group (82%) p=0.11. No secondary reactivation was seen in any patient in the treatment group. No infusion-related toxicity was seen in any treated patients. We have now extended these studies to recipients of VUD transplants in whom no CMV-CTL are detectable within the first 100 days of stem cell infusion. Tetramer-selected CMV-CTL have been adoptively transferred into six patients undergoing transplantation from an unrelated donor. CMV-CTL were given either for treatment of refractory CMV infection (n=5) or prophylactically 21 days post SCT (n=1). A cell dose of between 6x102/kg and 1.25x105/kg was administered with median purity of 95% of the infused T cell dose. No infusional toxicity or acute graft-versus-host disease was noted. CMV-CTL were not present in any patient prior to therapy. Within 7 days of adoptive transfer CMV-CTL were detectable in all patients comprising 0.6% – 20% of CD8+ T cell compartment. All patients demonstrated a reduction in the viral load and 5/6 cleared their viremia. In the patient who received prophylactic therapy durable expansion of CMV-CTL were observed up to 20% of CD8+ T cell pool. Taken together these data are consistent with the hypothesis that antigen-specific CMV specific CTL can be safely infused to recipients of VUD SCT and expand directly in vivo. Such an approach has considerable potential in the treatment or prophylaxis of CMV infection in patients undergoing VUD SCT.

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