Use of CD19-targeted immune modulation to eradicate AAV-neutralizing antibodies

Neutralizing antibodies (NAbs) against adeno-associated virus (AAV) represent a significant obstacle to the efficacy of systemic recombinant AAV vector administration or re-administration. While there are some promising preclinical immunomodulation strategies in development, insights into which B cell subsets and compartments maintain persistent AAV NAb may define the optimal eradication strategy. Given the limited success of CD20-directed monotherapy in previous studies, we hypothesized that CD19-directed approaches that extend targeting into the plasma cell compartments may improve AAV NAb eradication. We tested this approach in mice using chimeric antigen receptor T (CAR-T) cells or monoclonal antibodies (mAbs). We observed that combination mAbs targeting CD19, CD22, CD20, or B220 in mice did not eliminate tissue-resident B cells and, correspondingly, did not deplete pre-existing high titer AAV8 NAb. In contrast, CD19 CAR-T therapy eliminated peripheral and tissue-resident B cells and plasma cells and resulted in a marked reduction or eradication of high titer AAV8 NAb that permitted successful transgene expression following systemic AAV8 re-administration in mice. This successful therapeutic approach in mice identifies the population and location of B cells necessary to reduce or eradicate AAV NAb sufficiently to permit successful transgene expression with systemic AAV vector administration.