June 15-16, 2001
Reported by Jules Levin
Both The Virus and The Person's Immune System Affect Hepatitis C Clearance and Response To Interferon Therapy
During the first day's proceedings, speakers Charles Rice and Patricia Farci (see Day 1 Report) discuss how the virus contributes to avoiding clearance and successful treatment. The viruses' genetic diversity and high replication rates (which make the virus more error prone to mutate) make HCV more able to persist & avoid clearance during acute infection. Virus is more able to be cleared by a person when it remains less genetically diverse. If it increases in diversity the person is less able to clear it. Similarly in chronic infection, patients who respond to interferon show a decrease in viral diversity and in the number of viral strains. But, patients whose original virus strains persist do not respond to therapy, suggesting resistant strains are already present prior to therapy.
During day 2 at this meeting the immune response to HIV was discussed as opposed to the virus influence. This is a review of Barbara Reherman's (NIH, Liver Diseases Section, NIDDK) discussion of the immune response to HCV. She said HCV has a remarkable ability to establish chronic clinically persistent infections in individuals whose immune systems are otherwise competent, as in HIV. Diagnosis of HCV is typically made after chronic or persistent infection because there are no clinically apparent symptoms in the majority of cases. As in other viral infections, the outcome of infection is likely to depend on kinetics of viral replication and infection of host cells (how the virus acts in a patient's cells). It's outcome will also depend on the quantitative & qualitative characteristics of the host's immune system. For example, does the person's immune response kick in strongly with HCV specific CD4 and CD8 cell responses; how does HCV infection of the liver cells affect the immune response or signalling sent out to the immune system. Is the signaling of a response encouraged or discouraged. Reherman went on to say that to develop effective vaccines and immunotherapies to prevent and cure hepatitis C it is important to characterize and understand immune responses and viral factors that help viral clearance, and encourage the immune system to deal in a positive way with the virus. Of course this is a big expectation. In HIV we are still trying to understand how to develop immune therapies. I think it's clear, however, that HCV is getting increasing attention for developing therapies. In fact, to some degree it appears as if research attention may be drawn away from HIV towards HCV.
Ray Chung (Mass General Hospital/Harvard Medical School) suggested from preliminary data that immune therapy may be a viable goal. HCV-specific cellular immune responses might help to contain the virus, but it's also been suggested that the immune response might contribute to liver damage. In analyzing the CD8 mediated immune response, Chung identified and reported on two individuals with a strong and persisent cellular immune response against HCV during chronic infection. Both persons also showed control of viral replication and no evidence of active liver disease. Chung concluded that this suggested an effective strong immune response can control HCV & may not cause liver damage, and therefore these findings provide evidence for a rationale to consider immunotherapy in chronic HCV. Again, in HIV we have been looking for immunotherapy without success but maybe we can have better luck in HCV.
IL-10 and IL-12 Study Results
Paul Pockros (Scripps Clinic) reported on a study of IL-12 that did not show benefit in HCV. 225 patients at 21 sites with a previous history of non-response to interferon or combination IFN+ribavirin were randomized to 500 mg/kg rIL-12 or placebo subcutaneous injections twice weekly for 12 weeks. All patients had an HCV-RNA >10 to the fourth c/ml (NGI), elevation of ALT>1.25 ULN, and liver biopsies demonstrating chronic HCV within 12 months. Hepatic Activity Index (HAI) was improved in some, worse in some, and unchanged in some, but treatment groups have yet to be unblinded so it's unkown if there's a relationship with IL-12. The study was stopped prematurely due to a lack of effectiveness seen at an interim analysis and adverse events causing a high dropout rate of 13% (29/225). A majority of patients experienced chills, fever, fatigue, headaches and arthralgias during treatment sometime. More serious adverse events included stomatitis (inflammation in the mouth) in 68 patients (30%) and peripheral edema (buildup of fluid) in 24 (10%). 14 serious adverse events occurred, of which 7 were related or possibly related to IL-12: profound cytopenia in 2 patients (ITP-1, profound neutropenia [reduced neutrophils]-1), ascites in 1 patient, severe depression requiring hospitalization in 1 patient, 1 patient with melana, and 1 each with constipation or abdominal pain requiring hospitalization. The end of treatment response was 7/160, and the sustained virologic response was 2/160 (1.2%).
Also revealed at this meeting was that IL-10 may not be a viable therapy for HCV> A prior pilot study showed improved histology but no HCV RNA benefit, but recent data reveals HCV RNA can increase due to IL-10 therapy.
Reherman reported that HCV specific antibodies are generally detected 7 to 31 weeks after infection and targeted against epitopes in all viral proteins (the immune system mounts an antibody response to HCV). Several studies have described neutralizing antibodies that are targeted against the envelope proteins. However, recovery from HCV has also been described in the absence of an antibody response to envelope proteins and HCV persistence (chronic infection) without sequence changes in the envelope proteins. Therefore, progression to persistent infection is most likely a multifactorial process depending on many aspects of virus-immune system interactions.
Strong CTL Response May Be Needed
Reherman reported that prospective analysis of the cellular immune responses of patients with clinically symptomatic, self-limited hepatitis C demonstrated strong Th1 dominated T cell helper and cytotoxic T cell (CTL) responses in the blood. This cellular immune response was targeted against virus epitopes in all structural and nonstructural proteins of the virus. This is similar to findings in HIV. In other patients, lack of such a response or an inability to maintain it for an adequate time was associated with chronic infection establishing itself. In chimpanzees the CTL response in the liver cells was stronger when virus was self-contained compared to development of chronic infection.
She reported that HCV specific cellular immune responses are maintained for decades after HCV recovery, sometimes in the absence of antibodies. These type of responses are relevant to the question of whether they may prevent persistent infection after re-exposure to HCV.
It appears that the immune system and its relationship to HCV is obviously not well understood. Reherman reported that in chronic HCV, virus specific T cells were present at low frequencies in the blood, but could be found. HCV specific T cells were more frequently found in the liver. She said the reasons for the relative weakness of the cellular immune response, that is unable to clear the virus, yet strong enough to contribute to chronic inflammatory liver injury, are not known. General immune tolerance or immunosuppression are unlikely to be the cause of HCV persistence since in the absence of liver cirrhosis, the majority of chronically infected patients display normal immune responses against other viruses.
Of course, it appears that HIV has a negative impact on the immune response to HCV in coinfected persons. HIV may further impair the immune response to HCV and this may contribute to HIV accelerating HCV progression. The affect of HIV on HCV progression appears very complicated. Some persons have end stage liver disease or cirrhosis with high CD4s and undetectable viral load. While, in theory doctors and researchers feel that patients with high CD4s and low HIV viral load should improve response to interferon+ribavirin therapy. It remains uncertain how HCV/HIV coinfected patients will respond to HCV therapy compared to mono-infected patients. Some patients are likely to respond as well, while others may not respond as well. A factor is the presence of genotype 1, as the prevalence of genotype 1 appears slightly higher among coinfected persons than HCV infected, due to data showing patients HIV-infected due to IVDU have higher prevalence of genotype 1.
Hyperimmune C Immunoglobulin
K Krawczynski (CDC) reported on the potential usefulness of using this immune therapy in HCV. He reported that early studies of posttransfusion non-A, non-B hepatitis showed that intravenous infusions of globulins, which may have contained anti-HCV, reduced the incidence and severity of the disease. More recently, a decreased number of preexisting and new HCV infections were observed among liver transplant recipients treated with hepatitis B immunoglobulin, which may have contained anti-HCV.
The existence of neurtalizing anti-HCV antibodies was documented in experimental studies, among which studies of infectivity in chimps provided compelling evidence that the neutralization of the epitopes located in the hypervariable region 1 of the HCV envelope that use the globulin preperations with high titered anti-HCV (HVIg) containing neurtalizing antibodies could modify virus replication and the clinical course of the infection.
Krawczynski reported that studies at the CDC of anti-HCV globulin preparations in chimps during acute infection showed HCIg significantly shortened the length of HCV viremia and prevented acute hepatitis. In 1 of the 2 treated chimps, HCV viremia reoccurred after anti-HCV infusions were discontinued. . In 2 of 3 chronically infected chimps, passive anti-HCV transfer decreased the rate of HCV replication (HCV RNA reduced) which returned to pre-treatment levels after infusions were stopped. The author concluded that additional trials are warranted and I think he said he was planning such trials.
Long Term Maintenance Therapy For HCV: IFN/RBV non-responders are responding to pegylated interferon; ribavirin monotherapy, phlebotomy and pentoxyfilline suggested as maintenance therapy
Results from several studies suggest that interferon may reduce risk for hepatocellular carcinoma (HCC, liver cancer) and improve liver histology (fibrosis, inflammation) whether or not a patient achieves a sustained virologic response. Doctors have been using maintenance interferon therapy (keeping patient on interferon, usually lower dose, with or without ribavirin for an ongoing period of time). Their goal is to slow or prevent disease progression, as a study from Mitch Shiffman shows may occur from using such maintenance therapy. Two large studies, including the HALT-C trial conducted by the NIH, are looking at this concept using Pegasys in a large number of patients to see if they can confirm that interferon maintenance therapy does in fact slow or stop HCV progression. A second study is looking at PegIntron for maintenance therapy.
Previous Non-Responders Can Respond To Pegylated Interferon
At this meeting, preliminary 20 week data was revealed showing promising data on another note. At week 20, 40% (59/146) patients who had previously not responded to interferon or IFN-ribavirin had negative HCV RNA. The question of whether these patients were IFN monotherapy or combination therapy failures was raised at the meeting. Adrian Di Bisceglie said that more patients had previously failed IFN+RBV, but he does not have the actual breakdown of the data showing how many had actually failed mono-or combination therapy. However, at the recent DDW conference, preliminary data showed the PegIntron+ribavirin was very promising in generating negative HCV RNA in previous non-responders to IFN+RBV. Also at DDW, Nezam Afdhal reported from a small study that previous non-responders to combination therapy could respond well to Pegasys: HCV RNA negative at week 24 was 9/30 (30%) and ALT was normal in 16/30 (53%) at week 24 for those receiving Pegasys+ribavirin.
Data was presented at this meeting showing phlebotomy improved ALT. The data slightly suggested that HCV RNA may improve from phlebotomy but it was very unclear if there was any HCV RNA benefit. Phlebotomy is removing blood by IV. I believe this notion is based on high levels of iron may be in blood of some HCV patients which may be harmful, and phlebotomy may reduce the higher iron levels.
Marc Ghany (NIH, Liver Disease Section, NIDDK) reported on two small pilot studies suggesting ribavirin monotherapy improves ALT. After 48 weeks 5/6 patients receiving RBV had normal ALT compared to 1/6 receiving placebo. RBV therapy also showed improved HAI (Hepatic Activity Index) and benefit to fibrosis. Patients receiving RBV showed no change in their fibrosis but patients on placebo showed a worsening of fibrosis. One of the concerns about long term use of RBV is an accumulation of iron overload. In addition, for patients with HIV coinfection long term use of RBV may not be tolerable as it may be harmful in causing anemia.
Gary Davis (University of Florida) spoke encouragingly about how fibrosis is reversible, referring to a 3TC study showing that in HBV. He discussed how pentoxyfilline, antioxidants and IL-10 may have anti-fibrosis effects. We already know about the negative results of IL-10 in raising HCV RNA (see above). He suggested that anti-oxidants such as vitamin E, milk thistle, and a far eastern herbal preparation (TJ9, sho-saiko-to) may improve fibrosis. However, study results using milk thistle appear to be mixed on whether or not they are actually helpful in HCV disease, but milk thistle does not appear to be harmful except possibly in HIV. In preliminary in vitro studies, there is a suggestion that milk thistle may interact with HIV medications. A NIH study should be ongoing looking at that.
Finally, presenters talked about two new ribavirin-like drugs in early development. Vertex Pharmaceuticals is in phase 2 studies with VX-497 which they say is safer than ribavirin in that it doesn't cause anemia and it is more potent than RBV. They are expected to start a phase 3 study in combination with interferon. ICN Pharmacueticals discussed their ribavirin-like new drug which is earlier pre-clinical development stages.