Vacunas para COVID-19: Estado actual y perspectivas para su desarrollo / COVID-19 vaccines: current status and perspectives for its development

Resumen La pandemia por SARS-CoV-2 evidencia la importancia del trabajo conjunto para el desarrollo de vacunas contra el virus, estas incluyen virus completos, subunidades, vacunas atenuadas, vectores virales y ácidos nucleicos, la mayoría de propuestas están basadas en subunidades proteicas. De los más de 115 candidatos reportados hasta abril, 73 se encuentran en estudios preclínicos, a junio la opción más avanzada se ubica en fase II/II, una en fase II, dos en fase I/II y cuatro en fase I. Los candidatos más avanzados son AZD1222 (AstraZeneca) basada en adenovirus recombinante para la proteína S (fase II/III); PiCoVacc (Sinovac Biotech) basada en virus inactivado (fase I/II); mientras que mRNA-1273 (Moderna) basada en ARNm para la proteína S, INO-4800 (Inovio Pharmaceticals) basada en DNA plasmídico para proteína S, Ad5-nCoV (Cansino Biologicals) basada en adenovirus tipo 5 expresando la proteína S, LV-SMENP-DC basada en células dendríticas con lentivirus para dominios de proteínas virales y aAPC patógeno-específica, basada en células presentadoras de antígenos con lentivirus para dominios de proteínas virales (ambas de Shenzhen Geno-Immune Medical Institute, se encuentran en fase I). La finalidad de este trabajo contrarreloj se dirige hacia el único objetivo de lograr un candidato a vacuna que demuestre seguridad y efectividad en el control y prevención del virus sorpresivo que dejó al descubierto que no hay enemigo pequeño o que mientras más pequeño más peligroso, pues el causante de COVID-19 no solo atacó la salud humana sino la economía del planeta y las costumbres y actividades rutinarias que desarrollaba la humanidad.

ABSTRACT The SARS-CoV-2 pandemic shows the importance of joint work for the development of vaccines against the virus, these include complete viruses, subunits, attenuated vaccines, viral vectors and nucleic acids, most of the proposals are based on protein subunits. Of the more than 115 candidates reported until April, 73 are in preclinical studies, as of June the most advanced option is in phase II / II, one in phase II, two in phase I / II and four in phase I. The candidates more advanced are AZD1222 (AstraZeneca) based on recombinant adenovirus for protein S (phase II / III); PiCoVacc (Sinovac Biotech) based on inactivated virus (Phase I / II); while mRNA-1273 (Modern) based on mRNA for protein S, INO-4800 (Inovio Pharmaceticals) based on plasmid DNA for protein S, Ad5-nCoV (Cansino Biologicals) based on adenovirus type 5 expressing protein S, LV- SMENP-DC is based on dendritic cells with lentiviruses for viral protein domains and pathogen-specified aAPC, based on antigen-presenting cells with lentiviruses for viral protein domains (Shenzhen Institute of Genoimmune Medicine, are in phase I). The purpose of this work against the clock is directed towards the sole objective of achieving a vaccine candidate who demonstrates safety and determination in the control and prevention of the surprising virus that revealed that there is no small enemy or that the smaller the more dangerous, because the cause of COVID-19 not only attacked human health but the economy of the planet and the customs and routine activities that humanity develops.

Cationic liposomes in double emulsions for controlled release.

Liposomes containing a model active component were entrapped within the internal aqueous phase (W(1)) of W(1)/O/W(2) double emulsions, thus providing a double-encapsulation system. Our motivation for the development of this system is to prevent liposomes from interacting with unfavorable physicochemical conditions and to optimize this system for dermal vaccine delivery. The choice of cationic liposomes is based on the fact that they have high penetration ability across the skin and hair follicles, and an adjuvant effect on the activation of antigen-presenting cells. Cryo-SEM images showed that liposomes are well encapsulated within the W(1) phase, indicating that most liposomes remain intact during the homogenization step of formulation fabrication. Freezing the n-hexadecane oil (O) phase of the double-encapsulation formulations preserved their stability during the storage, and subsequent oil-thawing induced progressive release of liposomes and their contents. The release mechanism upon the freeze-thaw treatment was internal coalescence followed by external coalescence. Our results also indicated that tuning the concentration of L-α-phosphatidylcholine (PC) lipid in the cationic liposomes can control the release rate from the double-encapsulation formulations.

Temperature-induced protein release from water-in-oil-in-water double emulsions.

A model water-in-oil-in-water (W1/O/W2) double emulsion was prepared by a two-step emulsification procedure and subsequently subjected to temperature changes that caused the oil phase to freeze and thaw while the two aqueous phases remained liquid. Our previous work on individual double-emulsion globules1 demonstrated that crystallizing the oil phase (O) preserves stability, while subsequent thawing triggers coalescence of the droplets of the internal aqueous phase (W1) with the external aqueous phase (W2), termed external coalescence. Activation of this instability mechanism led to instant release of fluorescently tagged bovine serum albumin (fluorescein isothiocyanate (FITC)-BSA) from the W 1 droplets and into W2. These results motivated us to apply the proposed temperature-induced globule-breakage mechanism to bulk double emulsions. As expected, no phase separation of the emulsion occurred if stored at temperatures below 18 degrees C (freezing point of the model oil n-hexadecane), whereas oil thawing readily caused instability. Crucial variables were identified during experimentation, and found to greatly influence the behavior of bulk double emulsions following freeze-thaw cycling. Adjustment of these variables accounted for a more efficient release of the encapsulated protein.

Induction of instability in water-in-oil-in-water double emulsions by freeze-thaw cycling.

Individual water-in-oil-in-water (W1/O/W2) double-emulsion globules loaded with fluorescently labeled bovine serum albumin (FITC-BSA) were optically monitored within cylindrical capillaries during freeze-thaw cycling. Coalescence of internal aqueous droplets (W1) and external aqueous phase (W2), termed external coalescence, was not observed before or during freezing of the oil phase (O). On the other hand, this instability mechanism was readily promoted during thawing. This realization confirms the previously suggested potential of W1/O/W2 double emulsions to trigger release upon oil thawing and demonstrates that it is a direct result of globule breakage through external coalescence. The presented results also identified a threshold in the relative W1 droplet size above which instability occurred, while smaller droplets remained unperturbed and therefore indicate that optimization of the delivery can be achieved by tuning the size of W1 droplets. In addition, we propose a possible explanation for the occurrence of instability during oil thawing and its dependence on the size of W1 droplets. Because this alternative globule-breakage mechanism simply uses temperature increase (solid-to-liquid-phase transition) as external stimulus, W1/O/W2 double-emulsion delivery systems can be easily tailored by choosing an oil phase with the appropriate phase-transition temperature.

Controlled release from a nanocarrier entrapped within a microcarrier.

This study illustrates the entrapment of the dye molecule fluorescein sodium salt (FSS) by hydrogel nanoparticles, which are in turn confined inside a water-in-oil-in-water double-emulsion globule, and its subsequent release by the action of the competing agent hydrochloric acid (HCl). Thus, a "double carrier" concept is being introduced in which a nanoscale delivery vehicle is being transported by a microscale delivery vehicle in order to simultaneously take advantage of both systems. This may facilitate storage and handling while protecting the active substance and improving its action upon application.