With the understanding of the complex interaction between the tumour microenvironment and immunotherapy, there is increasing interest in the role of immune regulators in the treatment of head and neck squamous cell carcinoma (HNSCC). Activation of T cells and immune checkpoint molecules is important for the immune response to cancers. Immune checkpoint molecules include cytotoxic T lymphocyte antigen 4 (CTLA-4), programmed death 1 (PD-1), T-cell immunoglobulin mucin protein 3 (TIM-3), lymphocyte activation gene 3 (LAG-3), T cell immunoglobin and immunoreceptor tyrosine-based inhibitory motif (TIGIT), glucocorticoid-induced tumour necrosis factor receptor (GITR) and V-domain Ig suppressor of T cell activation (VISTA). Many clinical trials using checkpoint inhibitors, as both monotherapies and combination therapies, have been initiated targeting these immune checkpoint molecules. This review summarizes the functional mechanism and use of various immune checkpoint molecules in HNSCC, including monotherapies and combination therapies, and provides better treatment options for patients with HNSCC.

This study investigates by experiment the global characteristics of both moderate or intense low-oxygen dilution (MILD) oxy-combustion and air combustion of firing light oil and pulverized coal in a pilot-scale furnace. There are three burner configurations used, i.e., (I) central straight (primary) jet + swirl (secondary) jet, (II) central straight (primary) jet + two side symmetrical (secondary) jets, and (III) central straight (primary) jet + side asymmetrical jet. The furnace centerline temperature, species concentrations, and exhaust emissions are measured and compared for the MILD and conventional combustion cases. For light oil and pulverized coal, the MILD air combustion or oxy-combustion occurs with burner II or III, while the conventional combustion takes place when using burner I. For the light oil, the MILD oxy-combustion can be reached even using pure oxygen. As the MILD combustion is reached, a fairly uniform temperature distribution and low emissions of NO and CO are obtained. Note that burner III produces the largest internal recirculation of the flue gas, lowest peak temperature, and most uniform temperature, whereas the opposite occurs for burner I. Importantly, the MILD combustion is found to reduce the NO emission much more effectively in the oxy-combustion case than in the air combustion case. Moreover, the appearance of the MILD combustion of light oil and pulverized coal differs from the invisible MILD combustion of gaseous fuels. Dark sparks from burning oil droplets or char particles are present in the MILD combustion of light oil or pulverized coal. It is also revealed that the char burnout under the MILD combustion is weaker than that under the conventional combustion.

The present study has numerically simulated the oxy-fuel combustion of a methane (CH 4 ) jet in hot coflow (JHC). The main objective is to investigate the influences of the oxygen (O 2 ) molar fraction (X O2 * ), temperature (T cof * ) and velocity (v cof * ) of the O 2 /CO 2 coflow on dimensions of the JHC reaction zone or flame. The simulations use the model of eddy dissipation concept (EDC) with the detailed chemical mechanism described by GRI-Mech 3.0. To validate the modeling, several air-fuel JHC flames are predicted under the same conditions of the work of Dally et al. [Proc. Combust. Inst. 2002, 29, 1147− 1154; the predictions match well with the measurements. Results suggest that, as either X O2 * or v cof * decrease or T cof * increases, the volume of the JHC reaction zone increases and hence the overall oxidation rate of CH 4 decreases. In particular, raising the coflow speed v cof * causes the flame to be significantly thinner but only slightly longer. It is also demonstrated that the oxy-fuel reaction zone is larger, and so, the temperature is lower than the air-fuel counterpart. Besides, under identical conditions, the oxy-fuel combustion produces more carbon monoxide than does the air-fuel combustion.

Through experiment and numerical modeling, this study investigated the establishment of moderate or intense low-oxygen dilution (MILD) combustion in a laboratory-scale furnace when fuel and air are fully premixed (FP), partially premixed (PP), or non-premixed (NP). Experiments were carried out at firing rates from 7.5 to 15 kW and equivalence ratios (Φ) ranging from 0.5 to 1. The furnace thermal fields and exhaust NO x emissions for the three mixing patterns were compared. Validated computational fluid dynamics was used to aid in better understanding the flow and compositional structures in the furnace. Natural gas was used as the fuel. The eddy dissipation concept (EDC) model and the GRI-Mech 3.0 mechanism were used. Additional chemical kinetics calculations were also performed to examine reaction pathways under the MILD combustion regime. Moreover, the characteristics of the reaction regime of MILD combustion were examined and are discussed in detail. Estimation of the initial jet momentum rate (J) showed that J FP > J NP > J PP , and consistently the recirculating rate of internal flue gas (K v ) was found to be in the order K v,FP > K v,NP > K v,PP . Correspondingly, the highest values of both furnace temperature and NO x emission were experimentally measured in the PP case, while the lowest values were found in the FP case. The measured NO x emission was negligibly low for the FP case. Numerical results revealed that in all the three cases of firing natural gas (FP, PP, NP), more than 80% of the total NO formation results from the N 2 O intermediate route while other NO mechanisms are unimportant. As Φ is increased from 0.5 to 1.0, both the measured and simulated NO emissions in the three cases initially increase and then decrease. Moreover, for Φ > 0.9, the NO-reburning reaction becomes significant and the resulting reduction of NO is notable. The rates of both turbulent mixing and chemical reaction were found to play a significant role in the structure and establishment of MILD combustion, with estimated Damkoḧler numbers in the range Da = 0.01−5.35.

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