Hematopoietic growth factors: frontiers for cure

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

Neutropenia can often be corrected by treatment with granulocyte-colony stimulating factor (G-CSF) and off-label use of commercial human G-CSF (HuG-CSF) is a commonly used treatment for neutropenic animals. However, long-term HuG-CSF treatment can be associated with adverse effects, including neutropenia. Here, feline (Fe) G-CSF was produced in Pichia pastoris, pegylated (Peg) FeG-CSF and tested in cats. A randomized controlled clinical trial was conducted to evaluate the efficacy of PegFeG-CSF compared to FeG-CSF or HuG-CSF in FIV-infected (n=14), FIV-uninfected healthy cats (n=19), and in HuG-CSF-induced neutropenic cats (n=4). Daily FeG-CSF doses induced higher neutrophil production than HuG-CSF after the second week of treatment (P ⩽ 0.002). Weekly doses of PegFeG-CSF induced higher neutrophil counts and showed greater sustained activity than weekly doses of FeG-CSF. PegFeG-CSF provided the most therapeutic and sustainable neutrophil production (P<0.001) in both FIV-uninfected and FIV-infected cats, without the development of neutralizing antibodies. Conversely, all HuG-CSF-treated cats developed neutralizing antibodies, suggesting cross-reactive antibodies to endogenous G-CSF in a majority of the cases with severe neutropenia. Strikingly, when PegFeG-CSF was used to rescue cats with HuG-CSF-induced neutropenia, clinically normal neutrophil numbers returned. Thus, PegFeG-CSF appears to be a superior treatment for neutropenia in feline patients.

FIV-infected cats respond to short-term rHuG-CSF treatment which results in anti-G-CSF neutralizing antibody production that inactivates drug activity

The hematological and virological effects of recombinant human granulocyte colony-stimulating factor (rHuG-CSF) were evaluated in feline immunodeficiency virus (FIV)-infected cats. Six age-matched, FIV-infected cats used in this cross-over study were injected subcutaneously with 5 microg/kg of rHuG-CSF daily for 3 weeks, while six control cats received a placebo. Five of six rHuG-CSF-treated cats had significant increases in neutrophil counts that peaked on days 11-21 of treatment. All rHuG-CSF-treated cats exhibited an increase in myeloid:erythroid ratios of the bone marrow cells without significant changes in lymphocyte, CD4 counts, CD4/CD8 ratios, RBC counts, FIV antibody titers, and FIV loads in peripheral blood, and without clinical and hematological toxicities. Five of six rHuG-CSF-treated cats developed antibodies to rHuG-CSF by 14-21 days of treatment, which correlated with decreasing neutrophil counts and increasing neutralizing antibodies to rHuG-CSF. Three cats re-treated with rHuG-CSF rapidly developed neutralizing antibodies to rHuG-CSF, while one cat also developed neutralizing antibodies to recombinant feline G-CSF (rFeG-CSF). Overall, rHuG-CSF treatment increased neutrophil counts in FIV-infected cats without affecting the infection status of cats. However, long-term use of rHuG-CSF is not recommended in cats because of the neutralizing antibody production to rHuG-CSF that affects the drug activity. In addition, a preliminary finding suggests that repeated treatment cycle can also induce cross-neutralizing antibodies to rFeG-CSF, which may potentially affect the homeostasis of endogenous FeG-CSF.

Effect of recombinant human granulocyte colony-stimulating factor (rhG-CSF) on leukocyte count and survival rate of dogs with parvoviral enteritis

Dogs with clinical signs consistent with parvoviral enteritis and leukopenia (total leukocyte count < 5.0 x 10(9) l(-1)) were included in this randomised double-blind study (treatment group: n = 22; control group: n = 21). The dogs in the treatment group received a subcutaneous daily injection of 10 microg kg(-1) of recombinant human granulocyte colony-stimulating factor (rhG-CSF) for 5 days. Clinical and blood investigations were performed prior to the first injection, daily during the treatment period and on the day after treatment ended, and then once more, 26 days after the first injection. During the study, no significant differences were found between the two groups with respect to survival rate (treatment group: 68 per cent; control group: 71 per cent, P > 0 4, Fisher-Test) and other clinical findings. Similarly the total leukocyte count, neutrophil count and other haematologic and biochemical parameters did not differ significantly between the groups, based on differences from initial values (P > 0 05). Consequently, the use of rhG-CSF in the treatment of dogs with parvoviral enteritis cannot be recommended.

The use of human hematopoietic growth factors (rhGM-CSF and rhEPO) as a supportive therapy for FIV-infected cats

Recombinant human GM-CSF (rhGM-CSF) and erythropoietin (rhEPO) were tested on chronically FIV-infected laboratory cats and uninfected specific-pathogen-free (SPF) cats. In Study 1, a total of eight cats (four cats per group of either infected or uninfected cats) received subcutaneous injection (twice a day) for 2 weeks with 5 microg/kg of rhGM-CSF, while seven cats (three SPF and four FIV-infected cats) served as the placebo-treated control cats. Four of eight rhGM-CSF-treated cats (two cats each from infected and uninfected groups) developed elevated WBC counts which peaked at Days 5-8 of treatment when compared to placebo-treated cats. The elevated WBC counts were attributed to the increase in either neutrophils, lymphocytes, eosinophils, monocytes, or their combinations. The RBC counts, platelet counts, and blood chemistry were not significantly affected by the treatment. Anti-rhGM-CSF antibodies were detected in six of eight rhGM-CSF-treated cats by Day 35 post-first treatment. All rhGM-CSF-treated infected cats but no placebo-treated infected cats had 1-2 log increase in FIV load in the PBMC during the treatment. In vitro studies suggest that rhGM-CSF has an effect on FIV replication in T cells but not in alveolar macrophages. Five of eight rhGM-CSF-treated cats had low-grade fever at 3-6 days of treatment. In Study 2, four cats per group of either infected or uninfected cats were treated (subcutaneously once a day) three times a week for 2 weeks with 100U/kg of rhEPO and monitored as before, while seven cats (three SPF and four FIV-infected cats) served as the placebo-treated control cats. All rhEPO-treated cats had a gradual increase in RBC, Hgb, and PCV counts which peaked at 2-4 weeks post-first rhEPO treatment, whereas none of the placebo-treated cats had significant increase in these parameters. The rhEPO-treated cats also developed elevated WBC counts consisting of either elevated neutrophils, lymphocytes, or their combination by 4 weeks post-first treatment but there was no statistical difference between rhEPO-treated and placebo-treated groups. None of the cats developed anti-rhEPO antibodies and no remarkable changes in blood chemistry, clinical signs, and FIV loads or FIV antibody titers were observed. Overall, rhEPO can be used safely on FIV-infected cats but the use of rhGM-CSF on FIV-infected cats should be performed with discretion.

Cytokines and anti-cytokine therapy: clinical potential for treatment of feline disease

Cytokines are soluble proteins produced by nucleated cells throughout the body. They have wide ranging effects on cell growth and differentiation, mediating immune responses, haemopoiesis and tissue repair. Advances in recombinant DNA technology have led to a vast increase in knowledge of their biological properties and subsequently their use in human clinical trials. The use of human cytokines in feline medicine has been of limited success as the action of cytokines is often species restricted or their activity may be neutralized due to antibody formation. Recently, however, many feline cytokines have been cloned which raises the possibility of their future use in the management and prevention of feline disease. Ultimately, they may find widespread clinical uses including the treatment of cancer, cytopenias and viral infections and as vaccine adjuvants.

Biological response modifiers: interferons, interleukins, recombinant products, liposomal products

The concept of enhancing the normal immune response against infections and neoplasms has been considered for decades. The administration of various natural and synthetic products to simulate systemic infections has largely given over to the idea that specific cytokines can be used effectively when administered systemically. Interferons, interleukins, and hematopoietic growth factors may offer substantial clinical benefit in chronic viral infections, and cancers such as osteosarcoma, melanoma, and lymphosarcoma. Erythropoietin has been shown to have great utility in the management of chronic renal failure. At this point in time, only recombinant products derived from humans are commercially available, and they are expensive and not licensed for use in companion animals. Nevertheless, these products may have significant clinical impact on several highly fatal disorders of dogs and cats. When administered systemically, cytokines perturb complex regulatory pathways, and serious side effects may occur. Innovative delivery methods, such as liposomes, gene therapy, and even oral administration may increase the therapeutic index of these molecules. Biological response modification, cytokine biology, and associated delivery systems are rapidly changing fields, and the small animal veterinarian will need to watch for significant advances in these areas over the next several years.