False-positive HIV-1 RNA detection after CAR-T cell therapy in a multiple myeloma patient: multi-assay comparison confirms dual-target cross-reactivity.

Chimeric antigen receptor T-cell (CAR-T) therapies, employing lentiviral vectors, may cause false-positive HIV-1 RNA results due to amplification of vector-derived sequences. We describe a case of a patient with multiple myeloma undergoing CAR-T therapy tested with two dual-target assays testing positive at low copies for HIV-1 RNA. A single-target assay consistently tested negative. HIV serological tests remained non-reactive. This case highlights the importance of assay target design in interpreting HIV RNA results after CAR-T therapy and supports the importance of serological tests and alternative methods to avoid misdiagnosis.