Fetal liver CD34+ contain human immune and endothelial progenitors and mediate solid tumor rejection in NOG mice

BACKGROUND

Transplantation of CD34+ hematopoietic stem and progenitor cells (HSPC) into immunodeficient mice is an established method to generate humanized mice harbouring a human immune system. Different sources and methods for CD34+ isolation have been employed by various research groups, resulting in customized models that are difficult to compare. A more detailed characterization of CD34+ isolates is needed for a better understanding of engraftable hematopoietic and potentially non-hematopoietic cells. Here we have performed a direct comparison of CD34+ isolated from cord blood (CB-CD34+) or fetal liver (FL-CD34+ and FL-CD34+CD14-) and their engraftment into immunocompromised NOD/Shi-scid Il2rgnull (NOG) mice.

METHODS

NOG mice were transplanted with either CB-CD34+, FL-CD34+ or FL-CD34+CD14- to generate CB-NOG, FL-NOG and FL-CD14--NOG, respectively. After 15-20 weeks, the mice were sacrificed and human immune cell reconstitution was assessed in blood and several organs. Liver sections were pathologically assessed upon Haematoxylin and Eosin staining. To assess the capability of allogenic tumor rejection in CB- vs. FL-reconstituted mice, animals were subcutaneously engrafted with an HLA-mismatched melanoma cell line. Tumor growth was assessed by calliper measurements and a Luminex-based assay was used to compare the cytokine/chemokine profiles.

RESULTS

We show that CB-CD34+ are a uniform population of HSPC that reconstitute NOG mice more rapidly than FL-CD34+ due to faster B cell development. However, upon long-term engraftment, FL-NOG display increased numbers of neutrophils, dendritic cells and macrophages in multiple tissues. In addition to HSPC, FL-CD34+ isolates contain non-hematopoietic CD14+ endothelial cells that enhance the engraftment of the human immune system in FL-NOG mice. We demonstrate that these CD14+CD34+ cells are capable of reconstituting Factor VIII-producing liver sinusoidal endothelial cells (LSEC) in FL-NOG. However, CD14+CD34+ also contribute to hepatic sinusoidal dilatation and immune cell infiltration, which may culminate in a graft-versus-host disease (GVHD) pathology upon long-term engraftment. Finally, using an HLA-A mismatched CDX melanoma model, we show that FL-NOG, but not CB-NOG, can mount a graft-versus-tumor (GVT) response resulting in tumor rejection.

CONCLUSION

Our results highlight important phenotypical and functional differences between CB- and FL-NOG and reveal FL-NOG as a potential model to study hepatic sinusoidal dilatation and mechanisms of GVT.

Treatment of Breast Cancer with Fibroblasts Transfected with DNA from Breast Cancer Cells

This investigation was based on the hypothesis that weakly immunogenic, breast cancer-associated Ags, the products of mutant or dysregulated genes in the malignant cells, will be expressed in a highly immunogenic form by semiallogeneic IL-2-secreting fibroblasts transfected with DNA from breast cancer cells. (Classic studies indicate that transfection of genomic DNA can stably alter both the genotype and the phenotype of the cells that take up the exogenous DNA.) To investigate this question, we transfected LM mouse fibroblasts (H-2k) modified to secrete IL-2 with genomic DNA from a breast adenocarcinoma that arose spontaneously in a C3H/He mouse (H-2k). To increase their nonspecific immunogenic properties, the fibroblasts were also modified before transfection to express allogeneic MHC determinants (H-2Kb). Afterward, the IL-2-secreting semiallogeneic cells were cotransfected with DNA from the spontaneous breast neoplasm, along with a plasmid (pHyg) conferring resistance to hygromycin. Pooled colonies of hygromycin-resistant cells were then tested in C3H/He mice for their immunotherapeutic properties against the growth of the breast neoplasm. The results indicated that tumor-bearing mice immunized with the transfected cells survived significantly longer than mice in various control groups. Similar beneficial effects were seen in C57BL/6 mice injected with a syngeneic breast carcinoma cell line (EO771) and semiallogeneic, IL-2-secreting fibroblasts transfected with DNA from EO771 cells. The immunity was mediated by CD8+ T cells since immunized mice depleted of CD8+ cells failed to resist tumor growth.

Resistance to Melanoma in Mice Immunized with Semiallogeneic Fibroblasts Transfected with DNA from Mouse Melanoma Cells

Tumor-associated Ags (TAA) that characterize a population of malignant cells are recognized by CTLs in the context of determinants specified by the MHC class I locus. Nevertheless, most progressively growing neoplasms do not induce antitumor immune responses that can control tumor cell growth. The TAA may be insufficiently antigenic. We found previously that immunization of mice with a cellular immunogen prepared by transfecting tumor DNA into allogeneic mouse fibroblasts resulted in strong antitumor immune responses that were specific for the type of tumor from which the DNA was obtained. Since the fibroblasts differed at the MHC from the immunized mice, we postulated that the immunogenic properties of the allogeneic transfected cells might be enhanced if the cells were modified to express syngeneic class I determinants. In a mouse melanoma model system, the H-2Kb gene was introduced into LM mouse fibroblasts (H-2k). Afterward, the cells were transfected with DNA from B16 melanoma cells (H-2b). The transfected cells were tested for their immunotherapeutic properties in C57BL/6J mice (H-2b) with melanoma. Mice with melanoma treated solely by immunization with the semiallogeneic transfected cells developed strong, long-term resistance to the growth of the tumor. In some instances, the mice survived indefinitely. Intact rather than disrupted transfected cells were required to induce the antimelanoma response, consistent with direct presentation of TAA by the transfected cells. The augmented resistance to melanoma in mice treated with the semiallogeneic transfected cells points toward an analogous form of therapy for cancer patients.