Proc Natl Acad Sci U S A. 2015 Apr 21;112(16):5005-10. doi: 10.1073/pnas.1500408112.

Effective and lesion-free cutaneous influenza vaccination.


Wang J1, Li B1, Wu MX2.
  • 1Wellman Center for Photomedicine, Massachusetts General Hospital, and Department of Dermatology, Harvard Medical School, Boston, MA 02114.
  • 2Wellman Center for Photomedicine, Massachusetts General Hospital, and Department of Dermatology, Harvard Medical School, Boston, MA 02114



The current study details efficient lesion-free cutaneous vaccination via vaccine delivery into an array of micropores in the skin, instead of bolus injection at a single site. Such delivery effectively segregated vaccine-induced inflammation, resulting in rapid resolution of the inflammation, provided that distances between any two micropores were sufficient. When the inoculation site was treated by FDA-approved nonablative fractional laser (NAFL) before insertion of a PR8 model influenza vaccine-packaged, biodegradable microneedle array (MNs), mice displayed vigorous antigen-uptake, eliciting strong Th1-biased immunity. These animals were completely protected from homologous viral challenges, and fully or partially protected from heterologous H1N1 and H3N2 viral challenges, whereas mice receiving MNs alone suffered from severe illnesses or died of similar viral challenges. NAFL-mediated adjuvanicity was ascribed primarily to dsDNA and other “danger” signals released from laser-damaged skin cells. Thus, mice deficient in dsDNA-sensing pathway, but not Toll like receptor (TLR) or inflammasome pathways, showed poor responses to NAFL. Importantly, with this novel approach both mice and swine exhibited strong protective immunity without incurring any appreciable skin irritation, in sharp contrast to the overt skin irritation caused by intradermal injections. The effective lesion-free cutaneous vaccination merits further clinical studies.

KEYWORDS: biodegradable microneedle; dsDNA; nonablative fractional laser

PMID: 25848020



Skin is a more potent site than muscle, because of a large number of antigen presenting cells (APCs) resident in the skin. In sharp contrast, there are few APCs in the muscle in homeostasis state. In accordance to this, intradermal vaccination has been found to induce more potent immune responses than that induced by intramuscular injections of various vaccines, including influenza, Rabies etc1. However two major obstacles hamper the clinical application of intradermal vaccination:

1) Intradermal injection of vaccines is frequently associated with local reactions. Bacillus Calmette–Guérin (BCG) vaccine, an attenuated vaccine used worldwide to prevent the infection of Mycobacterium Tuberculosis (TB), should be administrated into skin to ensure its efficacy. However the vaccination of BCG always induces severe local reactions, generating permanent scars on the skin2. Moreover injection of influenza vaccines into skin by hypodermal needles caused swelling and erythema lasting for several days3, 4.

2) There is a lack of safe adjuvants for intradermal vaccination. Adjuvants could augment vaccine-induced immune responses, as well as modulate the type of immune responses. For example, Th1 immune responses are preferred to control intracellular pathogens infection (virus, intracellular bacteria etc), whereas Th2 immune responses are critical in the defense against extracellular pathogens (extracellular bacteria etc). Unfortunately previous studies showed that most currently used or under developed adjuvants, including alum adjuvant, oil-in-water emulsion and toll-like receptor agonists, were not suitable for cutaneous vaccination, because these foreign chemicals often induce severe and long lasting local reactions after injection into the skin5, 6.

In this study, Wang et al introduced two concepts, “fractional vaccine delivery” and “micro-sterile inflammation array” to solve these issues.

They first fabricated a biodegradable microneedle array to fractionally deliver vaccine into hundreds of mini spots instead of injecting vaccine into one large spot (Figure 1). Their study showed the fractional delivery of BCG vaccine as well as influenza vaccine by microneedles resulted in improved skin conditions as compared with intradermal injections (Figure 2).



Figure 1 Fractional delivery of vaccines into skin by the biodegradable microneedle array.


To address safety issue of adjuvant, they used inherent “danger signals” to alert the immune system instead of injecting foreign chemicals into the body. The inspiration came from a widely used adjuvant, aluminum hydroxide (Alum). A number of studies suggested the mechanism underlying Alum adjuvant owing to the death of host cells. Dead cells release “danger signals”, including uric acid, genomic DNAs etc, to activate a number of immune pathways, like inflammasome and nucleic acid sensing pathway, inducing sterile inflammation that could subsequently enhance the adaptive immune responses 7-9.



Figure 2 Combination of biodegradable microneedle array and NAFL adjuvant resulted in a lesion-free and effective vaccination.


Instead of enrolling foreign chemicals, Wang et al used non-ablative fractional laser (NAFL) to controllably induce the death of skin cells, releasing “danger signals” to immune systems. The NAFL generates an array of micro-injured zones each as small as 200 micrometers in diameter rather than damage a single large area of skin as illustrated in Figure 2. These micro-injured zones induce tiny sterile inflammation zones well separated by healthy skin and these tiny sterile inflammation zones can be resolved quickly, ensuring its safety10. Interestingly, this transient inflammation is sufficient to enhance the immune responses induced by a number of vaccines, including model vaccine ovalbumin, Hepatitis B vaccine, and influenza vaccines. Vaccination of influenza vaccine with this micro-sterile inflammation array induced more potent protection against a viral challenge10. The further investigation revealed that dsDNA released by laser-damaged host cells is one of the major mechanisms underlying NAFL-induced adjuvanicity.

Combination of “fractional vaccine delivery” and “micro-sterile inflammation array” resulted in more effective vaccination as compared to traditional intramuscular vaccination with little cost of safety. In addition, NAFL broadens the protection spectrum of microneedle-delivered influenza vaccines. This vaccination strategy not only fully protected mice from the challenge of the homologous virus strain, but also resulted in a significantly higher survival rate when challenged by genetically distant H1N1 strain and heterosutypic H3N2 strain. Cross-protective immunity is extremely important for seasonal influenza vaccines because the mismatch between vaccine viral strains and circulating viral strains occurs frequently, reducing the efficacy of seasonal influenza vaccines substantially. Such a mismatch took place recently in the flu season of 2009-2010, 2012-2013, and 2014-2015, diminishing the efficacy of vaccines, especially in elderly population (>65 years of age)11, 12.

The strategy hold a great promise to solve several key issues in today’s vaccine field, leading to safer and more efficient vaccination. Because these concepts/strategies were only tested in mouse and pig models, a more clinical relevant model like monkeys and clinic trials are expected in the near future to fully realize their potentials.



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