| Summary: | The aim of this study was to establish a pre-clinical SCID mouse model of PTLD in which to test CTL immunotherapy. EBV <i>in vitro</i> infected B lymphoblastoid cell lines (BLCLs) were used to give rise to PTLD-like lesions in SCID mice. A minimum dose of 2x10<sup>6</sup> BLCL cells consistently induced subcutaneous (sc) or Intraperitoneal (ip) human CD45+ve, CD20+ve B immunoblastic tumours <i>in vivo</i> within 5-7 weeks. Tumours expressed EBV-encoded small RNAs (EBERs) EBV nuclear antigen (EBNA)2 and latent membrane protein (LMP)1 suggestive of unrestricted viral gene expression. The phenotype of the lesions mirrored PTLD, and they were used for testing CTL immunotherapy. Intravenous inoculation of 2 doses of 4x10<sup>6</sup>-8x10<sup>6</sup> autologous CTLs a week apart significantly delayed sc tumour progression in sc BLCL-injected SCID mice (p=0.01). Similarly, ip transfer of 1 dose of 40xs10<sup>6</sup>-50x10<sup>6</sup> autologous CTLs or 3x10<sup>6</sup>-50x10<sup>6</sup> CD8-enriched T cells, into ip BLCL-inoculated animals significantly delayed tumour development <i>in vivo</i> (p=0.001 for both), and prevented tumour formation in a significant proportion (40%) of mice inoculated with CD8-enriched T cells (p=0.001). Immunostaining showed human T cells in the SCID tumours following CTL therapy, and that the cytotoxic mechanisms involved perforin and granzyme B cytotoxic molecules. Whilst CD4-enriched T cells significantly facilitated tumour outgrowth in sc BLCL-injected mice (p=0.04), they did not have a significant impact on tumour development in ip BLCL-inoculated animals. IL7 and 15 conditioning of CTLs <i>in vitro</i> prior to ip transfer into SCID mice significantly delayed ip BLCL-derived tumour formation <i>in vivo</i> when compared to CTLs expanded <i>in vitro</i> using standard methods involving IL2 stimulation (p=0.04). We conclude that PTLD can be modelled in SCID mice. In the animals, autologous CTLs and CD8-enriched T cells have a significant capacity to hinder PTLD-like tumour development.
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