A Novel Model of SCID-X1 Reconstitution Reveals Predisposition to Retrovirus-induced Lymphoma but No Evidence of γC Gene Oncogenicity

Abstract

The emergence of leukemia following gene transfer to restore common cytokine receptor gamma chain (gammaC) function in X-linked severe combined immunodeficiency (SCID-X1) has raised important questions with respect to gene therapy safety. To explore the risk factors involved, we tested the oncogenic potential of human gammaC in new strains of transgenic mice expressing the gene under the control of the CD2 promoter and locus control region (LCR). These mice demonstrated mildly perturbed T-cell development, with an increased proportion of thymic CD8 cells, but showed no predisposition to tumor development even on highly tumor prone backgrounds or after gamma-retrovirus infection. The human CD2-gammaC transgene rescued T and B-cell development in gammaC(-/-) mice but with an age-related delay, mimicking postnatal reconstitution in SCID-X1 gene therapy subjects. However, we noted that gammaC(-/-) mice are acutely susceptible to murine leukemia virus (MLV) leukemogenesis, and that this trait was not corrected by the gammaC transgene. We conclude that the SCID-X1 phenotype can be corrected safely by stable ectopic expression of gammaC and that the transgene is not significantly oncogenic when expressed in this context. However, an underlying predisposition conferred by the SCID-X1 background appears to collaborate with insertional mutagenesis to increase the risk of tumor development.

Thymic expression of a T-cell receptor targeting a tumor-associated antigen coexpressed in the thymus induces T-ALL

“…To explore the potential for survivin-reactive TCRs to mediate antitumor effects, we generated TCR-Tg mice expressing a TCR with specificity for an H-2b-restricted peptide in murine survivin (Sur [20][21][22][23][24][25][26][27][28] Figure 1A). Sur-TCR-Tg T cells, but not WT cells, specifically proliferated (supplemental Figure 1A, available on the Blood Web site) and degranulated ( Figure 1B), as evidenced by surface expression of CD107a, 31 in response to Sur [20][21][22][23][24][25][26][27][28] .…”

“…17,18 One possible explanation for these findings is a contribution of IL2Rgc signaling in early thymocytes to leukemogenesis, a hypothesis that remains controversial. [19][20][21] TCR signaling during early thymopoiesis appears sufficient to induce T-ALL in some animal models, and in others the aberrant TCR signal plays a cooperating role as part of an oncogenic cascade. [22][23][24][25] Interestingly, T-ALL induced in patients receiving IL2Rgc-expressing hematopoietic progenitors was associated with other oncogenic mutations, in particular those involving the NOTCH1 oncogene.…”

“…Sequence-validated purified PCR products were cloned into a human CD2 minigene-based vector as previously described 30 (kindly provided by Al Singer, NCI, National Institutes of Health [NIH]), and coinjected into fertilized C57BL/6 embryos yielding 11 transgenic founder lines. Three founder lines with a high frequency of Sur [20][21][22][23][24][25][26][27][28] tetramer-binding CD8 1 T cells were bred, housed at the NIH, and underwent further analysis.…”

“…To generate Sur-TCR-Tg mice, C57BL/6 mice were vaccinated twice 1 week apart with 100 mL of a Db-binding peptide derived from mouse survivin [20][21][22][23][24][25][26][27][28] extracted, and TCR a-and b-chains were cloned using 59-rapid amplification of cDNA ends (Life Technologies). TCR a-and b-transcripts were found to be Va8/Ja24/Ca and Vb13/Db2/Jb2/Cb2.…”

Recent Advances in Hematopoietic Stem Cell Gene Therapy

“…When the CD2-γc chain gene was expressed in transgenic mice, a few abnormalities involving T cells were observed, but tumorigenesis was not observed and T and B cell functions were recovered in γc chain-gene deficient mice. This study demonstrated that when the γc c chain gene is expressed externally, SCID-X1 may be treated safely [61].…”