Mutant/mutation
In the mutant the csp gene has been replaced with a mutated csp gene encoding CSP in which the amino acids SYIPSAEKI were replaced by the H-2-K^b-restricted CD8⁺ T-cell epitope of ovalbumin (SIINFEKL). 
SYIPSAEKI of CSP is the immunodominant H-2-K^d-restricted CD8⁺ T-cell epitope of CSP. The replacement with SIINFEKL allowed for recognition in H-2-Kb-carrying C57Bl6 mice.

Protein (function)
The CS protein is the major protein on the surface of sporozoites and is critical for development of sporozoites within the oocysts and is involved in motility and invasion of both the salivary gland of the mosquito and the liver cells. The protein is also found on the oocyst plasma membrane and on the inner surface of the oocyst capsule. Specific motifs in CS are involved in sporozoite binding to mosquito salivary glands and in sporozoite attachment to heparan sulfate proteoglycans in the liver of the mammalian host. During substrate-dependent locomotion of sporozoites, CS is secreted at the sporozoite anterior pole, translocated along the sporozoite axis and released on the substrate at the sporozoite posterior pole. Following sporozoite invasion of hepatocytes, the CS is released in the host cell cytoplasm.

Phenotype
The resulting parasites showed a phenotype comparable to WT parasites, with comparable mosquito infectivity and number of salivary gland sporozoites, functional sporozoite motility and normal invasive capacity and development inside hepatocytes. Thus, the introduced mutations to generate CSP^SIINFEKL parasites did not interfere with the completion of the life cycle, in either mosquito vector or mouse. All C57BL/6 mice that received 800 sporozoites of CSP^SIINFKEL intravenously developed a detectable (patent) blood stage infection by day 4, comparable to infection with WT sporozoites

Additional information
From the Abstract:
'We engineered Plasmodium berghei parasites that harbour a well-characterised epitope for stimulation of CD8+ T cells, either as an antigen in the sporozoite surface-expressed circumsporozoite protein or the parasitophorous vacuole membrane associated protein upregulated in sporozoites 4 (UIS4) expressed in exo-erythrocytic forms (EEFs). We show that the antigen origin results in profound differences in immunogenicity with a sporozoite antigen eliciting robust, superior antigen-specific CD8+ T-cell responses, whilst an EEF antigen evokes poor responses. Despite their contrasting immunogenic properties, both sporozoite and EEF antigens gain access to antigen presentation pathways in hepatocytes, as recognition and targeting by vaccine-induced effector CD8+T-cells results in high levels of protection when targeting either antigen. Our study is the first demonstration that poorly immunogenic EEF antigens do not preclude their susceptibility to antigen-specific CD8+ T-cell killing.'

Other mutants