It's a bidirectional level translator. Assuming DTR is high: If the PIC pulls the data line (the emitter of Q2) low to -5V, the base-emitter is forward biased and the collector is pulled down to ~-5V also. If the PIC doesn't pull the emitter low (-5V), or sets it high (0V), then there is no bias for the transistor and it won't be conducting and the collector voltage will be set by DTR.
If DTR is low, the transistor base-collector is forward biased, and the emitter is pulled low.