B2M and obesity due to melanocortin 4 receptor deficiency: To further investigate the therapeutic potential of specific interventions for B2M expression in adipose tissue during obesity, we employed an adipose-targeted adeno-associated virus type 9 (AAV9) vector carrying B2m-shRNA (AAV9-B2m) or ZsGreen (AAV9-null control) (Fig. 7a, b).