Experimental infection and protection against ... - TI Pharma

NF135.C10: a new Plasmodium falciparum clone for controlled human malaria
infections
and heterologous (NF54 infected/NF135.C10 stimulated, NF135.C10
infected/NF54 stimulated) in vitro re-stimulation (Figure 3D-I). IL-2
responses seemed slightly higher when stimulated with NF135.C10 but this was
similar for NF135.C10 and NF54 infected volunteers. IFNγ-producing cells were
found in both the innate compartment (γδ-T, NK, NK-T) and the adaptive
compartment (CD4 and CD8) and mainly displayed an effector memory
phenotype (Figure 4). Despite inter-individual differences in relative contribution
of various subsets, the composition of responding cells was highly consistent
over time for every individual (data not shown). Upon homologous restimulation
of cells on C+35, the vast majority of responding lymphocytes were
single positive for IFNγ (mean 71%), TNF (9.4%) or double positive for IFNγ and
TNF (18%). Additional responding lymphocytes were single positive for IL-2
(0.40%), double positive IFNγ + IL-2 + (0.21%) or IL-2 + TNF + (0.61%) or triple
positive (0.50%) (data not shown).
Discussion
We identified and characterized NF135.C10 as the first Pf clone of Asian origin
for successful infection of malaria-naive human volunteers by CHMI. Clone
NF135.C10 consistently produced gametocytes in culture, and was able to
generate infections in laboratory-reared mosquitoes with high yields of
sporozoites. NF135.C10 parasites were clearly distinct from NF54 parasites by
drug sensitivity and established genetic marker profiles. Clinical presentation
after CHMI and characteristics of PfRBC-specific recall (T-)lymphocyte responses
in vitro were similar to NF54.
Selection and identification of field strain parasites for CHMI poses technical
difficulties, because of insufficient and unstable production of infectious sexual
and sporogonic stages. For manufacturing purposes, cultures should ideally
produce gametocytes that consistently infect at least 75% of the mosquitoes
with at least ten oocysts resulting in 10-30 thousand sporozoites/mosquito. Only
after extensive effort on more than seventy isolates were we able to successfully
identify a parasite clone, NF135.C10, that met these criteria. Until now, the
culture of NF135.C10 has only been re-started (using previous cryopreserved
batches) seven times, as compared to 306 times for the NF54, and is therefore
more closely related to the original clone. Also the geographical and molecular
divergence from the NF54 strain makes this new clone an attractive candidate
for use in CHMI trials. The vast majority of CHMI trials have been carried out
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