Letermovir for Secondary Prophylaxis of Cytomegalovirus Infection and Disease after Allogeneic Hematopoietic Cell Transplantation: Results from the French Compassionate Program.

Letermovir potently inhibits the cytomegalovirus (CMV)-terminase complex. Letermovir primary prophylaxis given for the first 3 months after allogeneic hematopoietic cell transplantation (HCT) has been shown to reduce clinically significant CMV infection and is well tolerated. Until now, only case reports or small retrospective series have been published on the use of letermovir for a secondary prophylaxis (SP) of CMV infection or diseases after HCT. Here we report the outcome of 80 consecutive CMV-seropositive adult patients included in the French compassionate program and who received letermovir as a SP after at least 1 CMV episode (infection or disease) since HCT. Letermovir was initiated at a median of 170 (49 to 1829) days after transplant and given orally for a median of 118 (26 to 396) days at the usual daily dose of 480 mg once daily and adjusted to 240 mg once daily when coadministered with cyclosporine. The donors were seronegative in 53% of the cases. Fifty patients had a current or previous graft-versus-host disease (GVHD) and 14 had experienced CMV disease since transplant. Four (5.5%) patients developed CMV breakthrough infections (n = 1) or diseases (n = 3) after the initiation of letermovir. In 3 of these 4 patients, further investigation of virologic resistance showed a CMV UL56 mutation C325Y or W, conferring the high-level letermovir resistance. One or more adverse reactions were declared by the local investigator in 15 (19%) patients. Only 2 patients stopped letermovir SP because of an adverse reaction (pruritus, 1; cytopenia, 1). In our experience, letermovir given as a SP may prevent a new CMV reactivation in a high-risk patient population and can be administered for several weeks, providing a bridge between the pre-emptive or therapeutic treatment of a CMV episode and CMV-specific immune reconstitution, giving time for tapering immunosuppressants. Prospective studies are required to confirm these results.