The present disclosure provides, among other things, immune suppression regimens for in vivo gene therapy and uses thereof. In various embodiments of the present disclosure, in vivo gene therapy includes delivery of at least one exogenous coding nucleic acid sequence to a stem cell of the subject. Success of in vivo gene therapy can be inhibited or reduced by immunotoxicity. The present disclosure provides compositions and methods, including among other things immune suppression regimens, that reduce immunotoxicity of in vivo gene therapy, e.g., in vivo gene therapy including administration of a viral gene therapy vector to a subject.