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"<p>Oncogenic retroviruses are a particular family of viruses that  can cause some types of cancer.</p><br /><p>Thierry Heidmann and his colleagues in the CNRS-Institut  Gustave Roussy and the Universit&eacute; Paris Sud 11 R&eacute;trovirus Endog&egrave;nes et El&eacute;ments  R&eacute;tro&iuml;des des Eucaryotes Sup&eacute;rieurs Laboratory have identified a &quot;virulence  factor&quot; that inhibits the host immune response and allows the virus to spread  throughout the body. This factor is a sequence of amino acids that is located in  the envelope protein of the virus.</p><br /><p>These scientists have also shown that once mutated to lose its  immunosuppressive capability, this envelope protein could serve as a basis for  the development of vaccines, ScienceDaily reported Feb. 15.</p><br /><p>These findings have been published online in the Proceedings of  the National Academy of Sciences.</p><br /><p>Retroviruses are viruses whose genome is made up of RNA. These  viruses are unique in possessing an enzyme that enables synthesis from this RNA  of a DNA molecule capable of integrating into the DNA of a host cell. The  retrovirus then uses the cell machinery to replicate. HIV is one of the  best-known retroviruses.</p><br /><p>Oncogenic retroviruses (or oncoretroviruses) are cancer-causing  viruses. Numerous oncoretroviruses are associated with animal diseases. In  humans, two retroviruses, called HTLV and XMRV, have been associated with a type  of leukemia and with prostate cancer.</p><br /><p>The French researchers have been working on the ability of  retroviruses to propagate and persist in their hosts by escaping the immune  system. They have studied the molecular basis of this process, and have shown  that it is driven by the envelope protein of these viruses.</p><br /><p>First of all, this protein has an essential &quot;mechanical&quot; role,  as it induces the fusion of viral particles with the target cell membrane, thus  allowing them to penetrate into the cell. Using a mouse model of infection with  a murine leukemia virus, the researchers showed that this envelope protein also  has a second role that is equally essential to viral propagation in the body: it  is immunosuppressive, or in other words it inhibits the host immune response in  a radical manner, affecting both the &quot;innate&quot; and &quot;adaptive&quot; immune  responses.</p><br /><p>The researchers succeeded in locating the domain responsible  for this property within the amino acid sequence of the envelope protein. This  domain, an authentic virulence factor, is a crucial element in the arsenal that  enables retroviruses to invade their host and produce their pathogenic effect.  It thus becomes a target of choice for the design of novel antiretroviral  therapeutic strategies, including vaccines. The results obtained by these  scientists mean it will be possible to follow this path.</p><br /><p>They were able to introduce targeted point mutations into the  envelope protein that could suppress its ability to inhibit the immune system  which, as expected, reacted much more effectively than with the non-mutated  protein, producing a high level of antibodies and inducing antiviral cellular  immunity.</p><br /><p>By working on this mutated protein, it should be possible to  develop vaccines for the future. Indeed, after the mouse model, the researchers  were able to show that the HTLV and XMRV retroviruses associated with human  diseases were both endowed with an immunosuppressive domain in their envelope  protein.</p>"^^<http://www.w3.org/2001/XMLSchema#string>
<http://vaccinenewsdaily.com/stories/510530750-researchers-find-secret-weapon-of-cancer-causing-retroviruses>