The present invention provides for inhibition or blockade of immunomodulatory cell receptors to facilitate improved or complete reconstitution of a human immune system in laboratory animals, improve animal health, and improve animal longevity. Thus, the invention relates generally to compositions and methods of generating and using transgenic non-human animals that are engrafted with a human hematopoietic system involving anti-CCR5 agents. In various embodiments, the human hematopoietic system engrafted transgenic non-human animals of the invention are useful as systems for the in vivo evaluation of the growth and differentiation of hematopoietic and immune cells, immune responses, vaccines and vaccination regimens, and human pathogens and production and collection of immune mediators, including human antibodies.
