Development of drug-resistant herpes simplex virus infection after haploidentical hematopoietic progenitor cell transplantation.

An unusually high incidence of acyclovir- and foscarnet-resistant herpes simplex virus (HSV) infection was noted after lymphocyte-depleted blood hematopoietic progenitor cell (HPC) transplantation from HLA-haploidentical family donors. Fourteen adults with hematologic malignancies underwent blood HPC transplantation from haploidentical family donors. Pheresis products were stringently depleted of T and B cells by immunomagnetic adsorption, and patients received no immunosuppression after transplantation. HSV reactivation occurred in all 7 evaluable HSV-1- or HSV-2-seropositive patients, at a median of 40 days after transplantation. Susceptibility testing of clinically resistant viral isolates demonstrated acyclovir resistance in all 5 cases tested. Second-line therapy produced only partial responses, and in vitro evidence of foscarnet resistance developed rapidly in all 3 patients treated with foscarnet. Healing of lesions coincided with T-cell recovery. The prolonged immunodeficiency associated with stringent lymphocyte depletion of the graft appears to strongly predispose to emergence of drug-resistant HSV. Furthermore, immune reconstitution is necessary for eradication of infection.