CD56 expression in feline lymphoid cells

Racing CARs to veterinary immuno-oncology

Chimeric antigen receptors (CARs) have demonstrated remarkable promise in human oncology over the past two decades, yet similar strategies in veterinary medicine are still in development. CARs are synthetically engineered proteins comprised of a specific antigen-binding single chain variable fragment (ScFv) fused to the signaling domain of a T cell receptor and co-receptors. Patient T cells engineered to express a CAR are directed to recognize and kill target cells, most commonly hematological malignancies. The U.S Food and Drug Administration (FDA) has approved multiple human CAR T therapies, but translation of these therapies into veterinary medicine faces many challenges. In this review, we discuss considerations for veterinary use including CAR design and cell carrier choice, and discuss the future promise of translating CAR therapy into veterinary oncology.

Cancer stem cell surface markers on normal stem cells

The cancer stem cell (CSC) hypothesis has captured the attention of many scientists. It is believed that elimination of CSCs could possibly eradicate the whole cancer. CSC surface markers provide molecular targeted therapies for various cancers, using therapeutic antibodies specific for the CSC surface markers. Various CSC surface markers have been identified and published. Interestingly, most of the markers used to identify CSCs are derived from surface markers present on human embryonic stem cells (hESCs) or adult stem cells. In this review, we classify the currently known 40 CSC surface markers into 3 different categories, in terms of their expression in hESCs, adult stem cells, and normal tissue cells. Approximately 73% of current CSC surface markers appear to be present on embryonic or adult stem cells, and they are rarely expressed on normal tissue cells. The remaining CSC surface markers are considerably expressed even in normal tissue cells, and some of them have been extensively validated as CSC surface markers by various research groups. We discuss the significance of the categorized CSC surface markers, and provide insight into why surface markers on hESCs are an attractive source to find novel surface markers on CSCs.

Experimental feline enteric coronavirus infection reveals an aberrant infection pattern and shedding of mutants with impaired infectivity in enterocyte cultures

Feline infectious peritonitis (FIP) results from mutations in the viral genome during a common feline enteric coronavirus (FECV) infection. Since many virological and immunological data on FECV infections are lacking, the present study investigated these missing links during experimental infection of three SPF cats with FECV strain UCD. Two cats showed mild clinical signs, faecal shedding of infectious virus from 4 dpi, a cell-associated viraemia at inconsistent time points from 5 dpi, a highly neutralising antibody response from 9 dpi, and no major abnormalities in leukocyte numbers. Faecal shedding lasted for 28–56 days, but virus shed during this stage was less infectious in enterocyte cultures and affected by mutations. Remarkably, in the other cat neither clinical signs nor acute shedding were seen, but virus was detected in blood cells from 3 dpi, and shedding of non-enterotropic, mutated viruses suddenly occurred from 14 dpi onwards. Neutralising antibodies arose from 21 dpi. Leukocyte numbers were not different compared to the other cats, except for the CD8⁺ regulatory T cells. These data indicate that FECV can infect immune cells even in the absence of intestinal replication and raise the hypothesis that the gradual adaptation to these cells can allow non-enterotropic mutants to arise.

Suppression of NK cells and regulatory T lymphocytes in cats naturally infected with feline infectious peritonitis virus

A strong cell-mediated immunity (CMI) is thought to be indispensable for protection against infection with feline infectious peritonitis virus (FIPV) in cats. In this study, the role of natural killer (NK) cells and regulatory T cells (Tregs), central players in the innate and adaptive CMI respectively, was examined during natural FIPV infection. When quantified, both NK cells and Tregs were drastically depleted from the peripheral blood, mesenteric lymph node (LN) and spleen in FIP cats. In contrast, mesentery and kidney from FIP cats did not show any difference when compared to healthy non-infected control animals. In addition, other regulatory lymphocytes (CD4+CD25−Foxp3+ and CD3+CD8+Foxp3+) were found to be depleted from blood and LN as well. Phenotypic analysis of blood-derived NK cells in FIP cats revealed an upregulation of activation markers (CD16 and CD25) and migration markers (CD11b and CD62L) while LN-derived NK cells showed upregulation of only CD16 and CD62L. LN-derived NK cells from FIPV-infected cats were also significantly less cytotoxic when compared with healthy cats. This study reveals for the first time that FIPV infection is associated with severe suppression of NK cells and Tregs, which is reflected by cell depletion and lowered cell functionality (only NK cells). This will un-doubtfully lead to a reduced capacity of the innate immune system (NK cells) to battle FIPV infection and a decreased capacity (Tregs) to suppress the immunopathology typical for FIP. However, these results will also open possibilities for new therapies targeting specifically NK cells and Tregs to enhance their numbers and/or functionality during FIPV infection.

Temporal association of large granular lymphocytosis, neutropenia, proviral load, and FasL mRNA in cats with acute feline immunodeficiency virus infection

During acute feline immunodeficiency virus-C(PGammar) (FIV-C-PG) infection, we observed that cats develop large granular lymphocyte (LGL) lymphocytosis concurrent with a marked neutropenia that is temporally associated with the rise and fall of FIV-C-PG proviral loads. LGLs, generally considered to be analogous to natural killer (NK) cells, can also be highly cytolytic CD8/CD57 T cells. Neutropenia has been reported during acute human immunodeficiency virus (HIV-1) infection, but there is a paucity of information describing the pathogenesis of this condition. During HIV-1 infection, LGLs have been shown to be both CD16(+) NK cells and CD8(+)/CD57(+) T cells, but an association with neutropenia has not been described. However, neutropenia with concurrent LGL lymphocytosis has been demonstrated in both LGL leukemia and common variable immunodeficiency syndrome in people, and in both syndromes, an increase in soluble Fas ligand (FasL) has been associated with neutrophil apoptosis leading to neutropenia. Flow cytometric analysis demonstrated increases in CD56 and CD8 peripheral blood cell surface expression during acute FIV-C-PG infection. Expression of FasL mRNA was increased at the same time points as these peripheral hematologic abnormalities, and also decreased as FIV-C-PG proviral load reached set point. We describe an interesting temporal association between innate immune responses and viral load during acute FIV-C-PG infection, which has similarities to HIV-1 infection and other immune dyscrasias of people, and which may contribute to the neutropenia and LGL lymphocytosis during FIV-C-PG infection.

Relative quantification of canine CD56 mRNA expression by real-time polymerase chain reaction method in normal tissues and activated lymphocytes

Real-time PCR was optimized for the quantification of canine CD56 mRNA expression. This study was conducted to easily quantify canine CD56 expression and to identify its expression in normal tissues, peripheral blood mononuclear cells and activated lymphocytes in dogs. This assay revealed the highest level of CD56 mRNA expression in the normal canine brain, followed by the lung, kidney and liver. CD56 mRNA expression level in peripheral blood mononuclear cells was considerably lower; among activated lymphocytes in vitro, CD56 mRNA expression was increased.

Feline lentiviruses demonstrate differences in receptor repertoire and envelope structural elements

Feline immunodeficiency virus (FIV) causes fatal disease in domestic cats via T cell depletion-mediated immunodeficiency. Pumas and lions are hosts for apparently apathogenic lentiviruses (PLV, LLV) distinct from FIV. We compared receptor use among these viruses by: (1) evaluating target cell susceptibility; (2) measuring viral replication following exposure to specific and non-specific receptor antagonists; and (3) comparing Env sequence and structural motifs. Most isolates of LLV and PLV productively infected domestic feline T cells, but differed from domestic cat FIV by infecting cells independent of CXCR4, demonstrating equivalent or enhanced replication following heparin exposure, and demonstrating substantial divergence in amino acid sequence and secondary structure in Env receptor binding domains. PLV infection was, however, inhibited by CD134/OX40 antibody. Thus, although PLV and LLV infection interfere with FIV superinfection, we conclude that LLV and PLV utilize novel, more promiscuous mechanisms for cell entry than FIV, underlying divergent tropism and biological properties of these viruses.