Pegylated feline granulocyte colony-stimulating factor increases neutrophil levels in cats

Recombinant feline herpesvirus-1 (FHV-1) expressing granulocyte colony-stimulating factor (G-CSF) exhibits enhanced protective efficacy in felines

Vaccine efficacy relies not only on antigens but also on immunomodulatory agents/adjuvants that are often used to stimulate the immune system and enhance the immune response. However, current immunomodulatory agents are used to increase the immune response induced by viral or bacterial inactivated vaccine antigens, bacterial toxoids or polysaccharides but not attenuated live viruses. Based on the immunomodulatory functions of G-CSF and the characteristics of feline herpesvirus-1 (FHV-1) as an expression vector, a recombinant virus expressing feline G-CSF (WH2020-ΔTK/gI/gE-G-CSF) was constructed. The growth dynamics of WH2020-ΔTK/gI/gE-G-CSF were similar to those of WH2020-ΔTK/gI/gE. Compared with kittens vaccinated with WH2020 Δ TK/gI/gE, felines inoculated with WH2020 ΔTK/gI/gE-G-CSF produced more neutralizing antibodies and neutrophils, further alleviating clinical symptoms after FHV-1 infection. Taken together, our results revealed the potential of G-CSF as an ideal immune potentiator that can augment immune responses to FHV-1 and even other attenuated live vaccines.

APB-F1, a long-acting feline granulocyte colony-stimulating factor fusion protein, created by exploiting FL335, a chimeric Fab specific for feline serum albumin

Off-label use of a human granulocyte colony stimulating factor (hG-CSF) has been allowed to treat dogs and cats with neutropenia. However, repeated administration of hG-CSF induces undesirable anti-drug antibody (ADA) responses, implying the necessity of animal-derived G-CSF as a therapeutic reagent, preferably with a long-acting capability. Herein, we generated a recombinant fusion protein by genetically combining FL335, a chimeric Fab specific for feline serum albumin (FSA), and feline G-CSF (fG-CSF), with the ultimate goal of developing a long-acting therapeutic fG-CSF for cats. The resulting FL335-fG-CSF fusion protein, referred to as APB-F1, was produced well as a functional form in a Chinese hamster ovary (CHO) expression system. In in vitro analyses, APB-F1 bound to FSA at high affinity (K_D = 400 pM) and possessed 0.78 × 10⁷ U/mg G-CSF biological activity, clearly proving its biological functionality. Pharmacokinetic (PK) and pharmacodynamic (PD) studies using healthy cats revealed that the serum half-life (t_1/2) of APB-F1 was increased five times compared with that of fG-CSF (t_1/2 = 13.3 h vs. 2.7 h) in subcutaneous (SC) injections. Additionally, APB-F1 induced a profound and sustained increase in white blood cell (WBC) and actual neutrophil count (ANC) up to 10 days, which was far superior to other G-CSF preparations, including filgrastim (Neupogen™) and even pegfilgrastim (Neulasta™). Conclusively, a long-acting fG-CSF with potent in vivo bioactivity was successfully created by using FL335; thus, we provided evidence that our "anti-serum albumin Fab-associated" (SAFA) technology can be applied reliably in developing valuable long-acting biologics in veterinary medicine.