It was also revealed from previous studies carried out in cutaneous and visceral leishmaniasis patients, that the humoral response induced was found to be specific for Leishmania histones since no cross reactivity of VCL sera with mammalian histones were observed. In the present study cloning, expression, purification and molecular characterization of these four histone proteins of L. donovani was reported for the first time. The situation has further worsened with the emergence of drug resistance in various regions of endemicity and improper chemotherapeutic treatment of visceral leishmaniasis. Current VL therapy is based on the long-term parenteral administration of pentavalent antimonials, which, despite being expensive and highly toxic, has been the standard treatment for over Calycosin
. Currently available drugs are not safe for long term continual use for being highly cost ineffective. Due to the lack of effective and low-cost treatments, it is imperative to develop an ideal vaccine which would be protective against VL. In current scenario, there has been significant progress in understanding the immuno-pathogenesis of leishmaniasis. The parasite antigen able to induce an immune response has been predominantly associated with the identification of Formononetin proteins that may be used for vaccine development. Most of the studies aimed at identifying antigens from Leishmania spp have searched for molecules with the ability to stimulate Th1-type responses, which are known to be the major defense mechanism against Leishmania infection. Histone proteins which play an important role in DNA packaging, transcription and gene regulation, have been reported previously as potent vaccine candidate against cutaneous and viscerocutaneous leishmaniasis, but their protective role against VL is still to decipher.