Progressive depletion of certain immune cell — CD4+ T-cell — populations along with impairment of cellular immunity is responsible for the onset of AIDS in the case of HIV-positive people. Now, researchers from the Indian Institute of Science (IISc) Bengaluru, have shown that two FDA-approved drugs (raltegravir and elvitegravir) used for treating HIV actually impairs the immune system to varying extents. Both these drugs are widely used and are part of the combination anti-retroviral treatment.
In the presence of the drug elvitegravir, the mature B cells responsible for immunity showed a reduction in animal studies. The reduction was pronounced — 70% of the mice studied showed a decrease in mature B cells.
The drugs target the HIV integrase protein that is responsible for the integration of viral DNA into human genome. HIV is a retrovirus which contains RNA instead of DNA. So when HIV infects human cells, the RNA is made into complementary DNA (cDNA) and this cDNA gets integrated into the human DNA. The viral DNA then makes copies of itself and then more viral particles are made, which then further infect more T cells.
Integrase and Rag1
Although integrase protein is specific to HIV, it shares structural and functional similarity with a protein present in humans called RAG1 (recombination activating gene 1). RAG1 is an integral protein of the immune system, and without it different antibodies cannot be developed leaving humans immune-deficient.
The team led by Prof. Sathees C. Raghavan from the Department of Biochemistry at IISc found that owing to the structural and functional similarity between the two proteins (RAG1 and integrase), the drugs designed to target HIV integrase protein can also bind and hamper the functions of RAG1 protein that is responsible for generation of antibody diversity leading to maturity of B cells of the human immune system. The results of the study were published in the journal Cell Death and Disease.
The researchers carried out in vitro studies using purified RAG proteins, and also studied the effects of the drug on human cell lines and on mouse models. In vitro studies showed the elvitegravir drug inhibiting binding and cleavage of human DNA in a dose-dependent manner. “Inside the lymphoid cells, DNA cleavage is important for the generation of antibody diversity. We found the drug significantly decreases the RAG1 function. When the drug binds to it and prevents DNA cleavage, it results in compromised antibody diversity,” says Prof. Raghavan.
While raltegravir drug did not cause significant inhibition of binding and cleavage of human DNA, these were impaired in the presence of elvitegravir drug. Cleavage inhibition was seen even at a low dosage of 50 microMolar, and “distinct” inhibition was seen when elvitegravir drug concentration was 200 microMolar.
“The structure of the two drugs is not the same. Elvitegravir drug probably binds tightly to RAG1 protein causing significant inhibition in cleavage,” says Namrata M. Nilavar from the Department of Biochemistry at IISc and one of the first authors of the paper. Mayilaadumveettil Nishana is the other first author of the paper.
“The elvitegravir drug caused significant effect on immune system when an extrachromosomal assay was used to study its effect inside the cells. We saw a threefold reduction in immune activity at 100 nanoMolar concentration and eightfold reduction at 1,000 nanoMolar concentration,” says Prof. Raghavan.
Mice were treated with eight doses of elvitegravir drug at comparable dosage as used in humans. “We looked at how the drug affects the growth of different stages of B cells, which are responsible for robust immune system,” he recalls.
“In about 70% of animals we found significant reduction in B cell population, while 30% animals remained unaffected.”
“More studies have to be done before we can say that continued use of elvitegravir drug by HIV positive people may be counterproductive,” says Nilavar.
“In humans, the duration of treatment is longer. So the damage may be much higher. Based on our study we can say that use of elvitegravir may have side-effects on the immune system. Therefore, patients undergoing the treatment need to be monitored with utmost care,” Prof. Raghavan stresses.