The Larval Specific Lymphatic Filarial ALT‐2: Induction of Protection Using Protein or DNA Vaccination

Abstract

Genes from the infective stage of lymphatic filarial parasites expressed at the time of host invasion have been identified as potential vaccine candidates. By screening an L3 cDNA library with sera from uninfected longstanding residents of an area endemic for onchocerciasis, so‐called “endemic normals” (EN), we have cloned and characterized one such gene termed the abundant larval transcript two (ALT‐2). The stage specificity of ALT‐2 gene transcription and protein synthesis was confirmed by PCR using gene‐specific primers, and by western blot analysis of protein extracts from various stages of the parasite life cycle using specific antisera. Significant differences in antibody response to the recombinant ALT‐2 were observed in endemic populations with differing clinical manifestations of lymphatic filariasis with an antibody response present in sera from 18 of 25 (72%) EN subjects compared to 9 of 25 (36%) with subclinical microfilaracmia (MF) and 14 of 25 (52%) of those with chronic lymphatic obstruction (CP) (P=0.01 for comparison of EN to CP or to MF). This differential responsiveness suggests that the protective immunity postulated to account for their uninfected status might be associated with a response to this protein. When the utility of ALT‐2 as a vaccine candidate was tested in a murine model using either recombinant protein or a DNA vaccine construct, statistically significant protection was observed when compared to a control filarial gene product expressed across all stages of the parasite lifecycle (SXP‐1; P=0.02 for protein and P=0.01 for the DNA vaccine) or compared to adjuvant alone. This level of protection indicates that this vaccine is a promising candidate for further development.

Cloning, expression and characterization of Brugia malayi abundant larval protein transcript-2 (BmALT-2) expressed in Pichia pastoris

“…The pathologic progression of this disease is intriguing and gruesome making it a difficult task to develop a vaccine against this multicellular parasite. Of the different vaccine candidates identified for lymphatic filariasis, the ALT-2 protein stands out as a remarkable one with no known homologue in mammalian hosts, imparting about 74% protection in jirds [13][14][15][16][17][18][19][20][21][22]. This study will lead to the development of commercial largescale production of BmALT-2 as an inexpensive vaccine candidate.…”

“…Bmalt-2 of B. malayi (accession number U84723) was a kind gift from Dr Thomas B. Nutman, National Institutes of Health, Bethesda, MD, USA. Bmalt-2 was cloned in pRSETB vector as described by Ramachandran et al [21]. Bmalt-2 was amplified from pRSETB/Bmalt-2 plasmid construct by polymerase chain reaction (PCR) (Applied Biosystems, Foster City, CA, USA) with PR DNA polymerase.…”

“…ALT-2 plays a role in the evasion strategy of the filarial nematodes by amplifying Th2 responses along with interfering signals necessary for the development of pro-inflammatory Th1 populations [12,15]. Earlier studies proposed BmALT-2 of B. malayi as a promising vaccine candidate with about 76% protection in animal models [12,[15][16][17][18][19][20][21][22]. Therefore, ALT-2 is considered the most potential vaccine candidate for lymphatic filariasis.…”

Granuloma Formation around Filarial Larvae Triggered by Host Responses to an Excretory/Secretory Antigen

“…It is interesting to note that Ramachandran et al (13) have found that normal individuals in an area of endemicity react to purified BmALT-2 more strongly than individuals with asymptomatic microfilaremia. One is tempted to speculate that the reason that individuals with asymptomatic microfilaremia harbor high worm burdens may be because of their inability to produce high-level antibody responses to this candidate antigen.…”

Immune response studies with Wuchereria bancrofti vespid allergen homologue (WbVAH) in human lymphatic filariasis

“…For example, abundant larval transcript (ALT) gene (Gregory et al 2000;Gnanasekar et al 2004;Ramachandran et al 2004), which, as the name suggest is abundantly expressed in L3 stages of the parasite, has been shown to provide significant levels of protection in animal models. Although the nature of protective immune responses is highly debated over several years (Peralta et al 1999;Ravindran et al 2000), the consensus is that the host immune responses play a major role in determining clinical manifestations of various groups (Frank and Grieve 1996;Helmy et al 2000).…”