Origin of the vasculature supporting growth of primary patient tumor xenografts

Abstract

BackgroundStudies of primary patient tumor xenografts grown in immunodeficient mice have shown that these tumors histologically and genetically closely resemble the original tumors. These patient xenograft models are becoming widely used for therapeutic efficacy studies. Because many therapies are directed at tumor stromal components and because the tumor microenvironment also is known to influence the response of a tumor to therapy, it is important to understand the nature of the stroma and, in particular, the vascular supply of patient xenografts.MethodsPatient tumor xenografts were established by implanting undisrupted pieces of patient tumors in SCID mice. For this study, formalin fixed, paraffin embedded specimens from several types of solid tumors were selected and, using species-specific antibodies which react with formalin fixed antigens, we analyzed the species origin of the stroma and blood vessels that supported tumor growth in these models. Additionally, we investigated the kinetics of the vascularization process in a colon tumor and a mesothelioma xenograft. In mice bearing a head and neck xenograft, a perfusion study was performed to compare the functionality of the human and mouse tumor vessels.ResultsIn patient tumors which successfully engrafted, the human stroma and vessels which were engrafted as part of the original tumor did not survive and were no longer detectable at the time of first passage (15–25 weeks). Uniformly, the stroma and vessels supporting the growth of these tumors were of murine origin. The results of the kinetic studies showed that the loss of the human vessels and vascularization by host vessels occurred more rapidly in a colon tumor (by 3 weeks) than in a mesothelioma (by 9 weeks). Finally, the perfusion studies revealed that while mouse vessels in the periphery of the tumor were perfused, those in the central regions were rarely perfused. No vessels of human origin were detected in this model.ConclusionsIn the tumors we investigated, we found no evidence that the human stromal cells and vessels contained in the original implant either survived or contributed in any substantive way to the growth of these xenografts.

Interrogating open issues in cancer precision medicine with patient-derived xenografts

“…However, to avoid immune rejection of xenotransplants by the host, PDX models are primarily generated by transplanting tumour fragments into immunodeficient mice. The absence of 15 many components of the immune system in these mice, and the loss of endogenous human immune cells upon propagation of the human tumour tissue over multiple passages 70,71 , limit the utility of such models to explore the role of the immune system in tumour progression and to test novel immune-based therapies 72 .…”

“…However, to avoid immune rejection of xenotransplants by the host, PDX models are primarily generated by transplanting tumour fragments into immunodeficient mice. The absence of many components of the immune system in these mice, and the loss of endogenous human immune cells upon propagation of the human tumour tissue over multiple passages 70,71 , limit the utility of such models to explore the role of the immune system in tumour progression and to test novel immune-based therapies 72 Although these procedures are known to cause severe graft-versus-host disease (GvHD) beginning 2-5 weeks after injection 73,74 , seriously limiting the useful investigative time window of these models and the translational value of these studies 75 , PBL and TIL mice can be used for cost-effective short-term testing of novel immune therapeutics and for assessing short-term adverse effects.…”

“…However, to avoid immune rejection of xenotransplants by the host, PDX models are primarily generated by transplanting tumour fragments into immunodeficient mice. The absence of 15 many components of the immune system in these mice, and the loss of endogenous human immune cells upon propagation of the human tumour tissue over multiple passages 70,71 , limit the utility of such models to explore the role of the immune system in tumour progression and to test novel immune-based therapies 72 .Humanized mice (also known as human haemato-lymphoid chimeric mice or human immune system (HIS) models) are immunocompromised mice in which selected immune components have been introduced to generate a competent human immune system with different degrees of immune reconstitution. One methodology for the generation of humanized mice involves the transplantation of total peripheral blood from healthy human donors or patients (peripheral blood lymphocyte(PBL) models) or, in particular applications, the infusion of tumour-infiltrating lymphocytes (TILs) (FIG.…”

AAV9 delivering a modified human Mullerian inhibiting substance as a gene therapy in patient-derived xenografts of ovarian cancer

“…Some of the limitations of PDXas are the serial passaging of the tumors, which can be lengthy and cause loss of clonal diversity, and replacement of human stroma and human vasculature (27,28). Methods that establish primary cell lines and PDXas in parallel allow for faster in vivo and in vitro testing that could direct therapeutic strategies for individual patients in real time (19,(29)(30)(31)(32), making ascites an ideal source of material for xenografts, which we distinguished from biopsy PDXs by referring to them as PDXas.…”

New cast for a new era: preclinical cancer drug development revisited

“…Direct analysis addressing the fate of stromal components of the original graft or stromal changes upon propagation are still warranted today (28). However, recent studies by Hylander et al demonstrated that the human microvasculature of a colon PDX is partially replaced by host vessels as early as three weeks (33). Additionally, Lin et al reported that more than 40% of analyzed pancreatic PDXs harbored less human than mouse DNA, supporting the presence of infiltrating murine cells (34).…”