Brief Updates
Adjuvants for Immunization Trials
Since it is not clear which mechanism are involved in parasite killing in
the two primary screens (Abraham's O. volvulus chamber model and
Lucius' A. viteae infection model) and since it is clear that the
types of immune response to antigens can be influenced/determined by adjuvants
given at the time of immunization, it has been decided that before individual
recombinant antigens are tested for their protective immune potential, both
primary screens will be assessed for their responses to the effects of different
adjuvants. After consultation with Bonnie Mathieson it was decided that
the following your "types" of adjuvants should be tested: BCG,
Ribi, block co-polymers and QS 21. Each of these adjuvants stimulated the
immune system somewhat differently from the others, and all represent classes
of adjuvants in which there likely will be additional refinements in the
future.
To determine which of these adjuvants is most effective in stimulating protective
immunity in these two screening models, experiments will be carried out
by David Abraham and Richard Lucius using either a cocktail of 4-6 recombinant
antigens (with unproven effectiveness) or an ES antigen derived from A.
viteae (of proven efficacy at least in the infection model). Experiments
to optimize the route of administration of the immunogen/adjuvant are being
carried out before the testing of individual recombinants.
L3 Supply
Milan Trpis who had been supply O. volvulus L3's at the rate of
almost 100,000 per year has switched his base of operations from Liberia
to Nigeria. While Milan is currently having some problems in Nigeria, it
is hoped these will soon be resolved and the Nigerian facility will be up
and running. In the meantime, Sarah Lustigman/Fred Prince have been able
to "fill the void" by supplying L3's from Liberia at approximately
the same rate of 150,000 per year. Both production facilities likely will
run in parallel at least for a time.
More than 400,000 O. volvulus L3's have been distributed to investigators
during the past five years. Currently, there are approximately 7,000 L3's
in the "bank", and several investigators are still awaiting L3's
they have already requested. Until supply exceeds demand, distribution will
be prioritized to keep the resource facilities (Abraham's screen, Lucius'
screen Tuan's morphologic localization) supplied. Every effort will be made
by the OTF to match requests and supplies. Almost 100,000 O. linealis
L3's (produced by Sparky Lok) have been supplied to investigators during
the past five years. Production of these larvae (which has turned out to
be even more difficult/costly than production of O. volvulus L3's)
has ceased. Approximately 10,000 larvae remain stored for future studies
that might become necessary when a protective immunogen active in the current
"primary" screens is considered for trials in a secondary cattle/O.
linealis screen.
New Strategic Plan
Anyone who has not received but would like a copy of the new Strategic Plan
should contact the EMCF.
Antigens available for Primary Screening
To date, antigens have been made available for screening from Ted Bianco
(B020), Jan Bradley (OV-11, OV-29), Sarah Lustigman (OV-7), Jim McKerrow
(MCKONCHO-1), Larry McReynolds (paramyosin), Fran Perler (01-3) and Tom
Unnasch (RAL2). Some of these likely will be pooled into a cocktail for
the adjuvant evaluation studies mentioned above, and when those technical
experiments are complete, these and other submitted antigens will be tested
for their protective immune potential in those screens.
rtPCR/cDNA Cloning meeting
On 2/24/92 John Donelson, Claude Maina, Larry McReynolds, Nithya Raghavan,
Alan Scott, Ted Bianco and Steve Williams met to evaluate the application
of current cDNA cloning technologies for use in the construction of Onchocerca
L3 libraries. The major recommendations of that meeting were as follows:
1) Top priority should be given to the construction of an L3 cDNA library
using conventional non-PCR technology.
2) Additional Onchocerca L3 larvae should be collected for construction
of several "activated" L3 libraries by rtPCR (reverse transcriptase
of RNA PCR). These libraries would be constructed using L3 larvae that have
been stored in culture medium for several hours to a few days. These "activated"
larvae may be producing mRNA transcripts that mimic gene expression of the
parasite in the human host. Collection of the larvae for this project should
be done only after sufficient larvae have been obtained for the non-PCR
library.
3) L3 larvae of other species of Onchocerca (such as O. lienalis)
should be collected for using techniques such as parasite lysis, RNA purification,
poly(A+) RNA isolation, cDNA synthesis and other steps required for efficient
construction of complete cDNA expression libraries.
4) Research should continue on the adaptation of rtPCR technology to the
construction of representative cDNA expression libraries. This would include
the optimization of all steps required in this complex process.
RFP (Request for Proposal) Letter
EMCF funding of onchocerciasis research is divided into three major categories:
provision of resources (L3 production, screening an antigen localization),
in vivo (especially human) studies of protective immunity, and isolation
and production of protective immunogens. The funding cycle for grants to
isolate and produce protective immunigens requires that RFP letters be sent
to interested investigators by June 15, 1992. These letters, describing
broadly the type of proposal being sought, will be sent from Joe Cook's
office. All those who attended the Wood's Hole meeting in April, 1991 will
receive these letters.
Eric A. Ottesen