Clustering and Erratic Movement Patterns of Syringe-Injected versus Mosquito-Inoculated Malaria Sporozoites Underlie Decreased Infectivity

Abstract

Malaria vaccine candidates based on live, attenuated sporozoites have led to high levels of protection. However, their efficacy critically depends on the sporozoites’ ability to reach and infect the host liver. Administration via mosquito inoculation is by far the most potent method for inducing immunity but highly impractical. Here, we observed that intradermal syringe-injected Plasmodium berghei sporozoites (syrSPZ) were 3-fold less efficient in migrating to and infecting mouse liver than mosquito-inoculated sporozoites (msqSPZ). This was related to a clustered dermal distribution (2-fold-decreased median distance between syrSPZ and msqSPZ) and, more importantly, a 1.4-fold (significantly)-slower and more erratic movement pattern. These erratic movement patterns were likely caused by alteration of dermal tissue morphology (>15-μm intercellular gaps) due to injection of fluid and may critically decrease sporozoite infectivity. These results suggest that novel microvolume-based administration technologies hold promise for replicating the success of mosquito-inoculated live, attenuated sporozoite vaccines. IMPORTANCE Malaria still causes a major burden on global health and the economy. The efficacy of live, attenuated malaria sporozoites as vaccine candidates critically depends on their ability to migrate to and infect the host liver. This work sheds light on the effect of different administration routes on sporozoite migration. We show that the delivery of sporozoites via mosquito inoculation is more efficient than syringe injection; however, this route of administration is highly impractical for vaccine purposes. Using confocal microscopy and automated imaging software, we demonstrate that syringe-injected sporozoites do cluster, move more slowly, and display more erratic movement due to alterations in tissue morphology. These findings indicate that microneedle-based engineering solutions hold promise for replicating the success of mosquito-inoculated live, attenuated sporozoite vaccines.

Artificial Intelligence‐Supported Video Analysis as a Means to Assess the Impact of DROP‐IN Image Guidance on Robotic Surgeons: Radioguided Sentinel Lymph Node versus PSMA‐Targeted Prostate Cancer Surgery

“…Registered coordinates of the DROP‐IN Probe tip allowed us to reconstruct its movement trajectory over time. In line with our previous works, [ 9,14b,16a,26 ] the digitized track allowed us to use custom algorithms (MATLAB, the MathWorks Inc., MA, USA) to extract kinematic metrics such as straightness index, angular dispersion, and adjusted speed. To eliminate the effect of camera location and zooming, the adjusted speed was considered as percentage of position change in each time point.…”

Ultra-low volume intradermal administration of radiation-attenuated sporozoites with the glycolipid adjuvant 7DW8-5 completely protects mice against malaria

“…We expect that these ultra-low volumes will still be necessary when scaling up ID-RAS to larger animal models or humans. Inoculation in ultra-low volumes improves spz motility in the skin and allows spz to efficiently invade blood vessels and lymph to home to the liver and dLN, respectively 34 . In our report, 2.5 µL was selected as the smallest volume that could be reliably prepared in the research laboratory for pre-clinical mouse injections.…”

“…Other studies have also suggested that the reason for ID spz administration failure may be due to the more tolerogenic environment of the skin, which could ultimately lead to more regulatory immune responses in the liver 25 , 30 . However, most of these studies used standard ID injection volumes (10–50 µL), which do not mimic the ultra-low volumes delivered by probing mosquitoes 31 , 32 , nor facilitate efficient exit of spz from the skin, since spz must move by contact-dependent motility 33 , 34 . Based on the available data, and recognition of this unique biology and motility requirements of spz, we hypothesized that two key aspects of RAS administration are critical for effective ID vaccination: 1) the injection volume must be compatible with the contact-dependent motility of the spz, and 2) the tolerogenic skin immune environment must be overcome.…”

Ultra-low volume intradermal administration of radiation-attenuated sporozoites with the glycolipid adjuvant 7DW8-5 completely protects mice against malaria

“…Other studies have also suggested that the reason for ID spz administration failure may be due to the spz inducing a more tolerogenic skin environment, which could ultimately lead to more regulatory immune responses in the liver [ 25 , 30 ]. However, most of these studies used standard ID injection volumes (10–50 μL), which do not mimic the ultra-low volumes delivered by probing mosquitoes [ 31 , 32 ], nor facilitate efficient exit of spz from the skin, since spz must move by contact-dependent motility [ 33 , 34 ]. Based on the available data, and recognition of this unique biology and motility requirements of spz, we hypothesized that two key aspects of RAS administration are critical for effective ID vaccination: 1) the injection volume must be compatible with the contact-dependent motility of the spz, and 2) the tolerogenic skin immune environment must be overcome.…”